A Treatise on the Incubus, or Night-Mare, Disturbed Sleep, Terrific Dreams and Nocturnal Visions

Amongst all the subjects of terror which infest the human mind, there is none so powerful as the idea, which is generally imbibed at a very early period of life, respecting ghosts and supernatural appearances; and there are comparatively few persons who, when alone and in the dark, are perfectly free from them. In sleep, however, we are all much more timid than when awake. I believe every person’s experience coincides in this opinion: hence it arises, that the idea of ghosts and spectres being the idea which inspires us with the greatest terror, is that which most readily and frequently presents itself to the mind, when the nervous system is suddenly agitated during sleep; a state when all objects of fear act with increased force. Whatever may be the cause which induces this kind of shivering during sleep, the shivering itself appears to me evidently to be the immediate cause of the terror, and the accompanying terrific dream; and this I conceive to happen from association; for as this shivering is the kind of involuntary sensation we feel when suddenly alarmed, or even when we hear or read a tale of terror, the feeling itself becomes so associated with terror, as always to recal to the mind, even in sleep, the idea of it; the sensation being the same as if the nerves had actually received some terrific impression; and as the imagination has full play when asleep, it is seldom long in furnishing the terrific object.

I have known these dreams to be succeeded by an hysterical affection, of involuntary laughing and crying; and they are, I believe, in all cases attended with a great degree of nervous irritability.

It will sometimes happen in this case, as in the preceding, that the patient does not awake from his dream, notwithstanding that his vociferations have been loud enough to wake all those who may sleep near him. When this happens he seldom or never has any recollection of his terror, and feels greatly surprised when told of the alarm he had given to others. The moment the shivering which produced the terror has ceased, this likewise ceases; and seldom leaves in the mind, any trace of its having existed: in this respect it differs greatly from the Night-Mare, in some others it appears to have some considerable affinity to that affection.

It is not uncommon for persons affected with these terrific dreams to leap out of bed, and attempt to escape from some imaginary danger by flight. Many instances have occurred of persons jumping immediately out of a high window under these circumstances: the same accident very lately occurred to a youth in this metropolis.

There are several other accidents to which our sleep is liable, but as they differ in their nature considerably from Night-Mare, we shall not here take any notice of them.

I shall now speak of the persons who are subject to Night-Mare, before entering into an investigation of its causes.

This affection may at some time or other occur to any person whatever, as it will for the most part be found to be the constant attendant upon indigestion: now the most healthy person in the world will sometimes meet with food which his stomach will not digest, and if he goes to sleep whilst such food is remaining in the stomach, or in the superior portion of the alimentary canal, he will certainly be affected with Night-Mare, to a greater or less degree. But a peculiar habit of body is necessary to render a person subject to it, so that it can become habitual. Many persons begin to feel its effects in very early youth; these are generally of a contemplative disposition, and of a peculiar temperament, which renders them liable to hypochondriasis and nervous diseases. To these persons the Night-Mare often becomes habitual. All who follow sedentary employments, or whose avocations keep them mostly in doors, more especially literary characters, and all studious persons, are the victims of these affections. Those likewise, who, although they do not want for air and exercise, yet are accustomed to a coarse and unwholesome diet; hence sailors are, of all classes of men, the most subject to Night-Mare and terrific dreams. All hypochondriacs, and frequently pregnant women, are amongst the subjects of these affections.

It occasionally accompanies fever and other acute diseases. I remember one patient to whom it became extremely troublesome in the last stage of consumption, who had never before in her life been affected by it. Sylvius Deleboe, who has recorded the history of an epidemic disease, which raged in the city of Leyden, in the year 1669, mentions the Incubus as a very common affection in it, with which he was himself afflicted to a great degree. He describes it as accompanied with an unusual degree of somnolency, and making its attack on the accession of the febrile paroxysm. Perhaps it was something of this kind, which Cœlius Aurelianus asserts to have been epidemic at Rome. Sylvius relates that the lethargy, or propensity to sleep, was so great during the febrile paroxysm, and accompanied with so unpleasant a sensation, even when Night-Mare did not come on, that he thought proper to order himself, as well as his patients, to be kept awake by the attendants. He describes it thus: “Non tantum cum Incubo, sed absque ipso gravis fuit ægris multis Somnus profundus, et insomniis multifariis molestus.” In another place, “Nec tantum sola difficili respiratione laborarunt multi, verum etiam Incubo nonnulli, et inter ipsos ego quoque; qui cum paroxysmis febrilibus repetens atque somnolentiam simul excitans, fuit mihi valdè molestus, donec ipsum agnoscens rogarem adstantes, ut tamdiu somnum in quem tam valde propendebam, interturbarent ac impedirent, donec paroxysmo declinante in somnum suavem ac commodum inciderem absque omni incubo.” Sylvii Praxeos. Med. Tract. x.

It sometimes appears in very early life, in which case it generally sticks close to the patient, almost all his days. In some, however, such a change in the constitution takes place at puberty as destroys altogether that predisposition to this affection, which existed in early life.

Females appear much less subject to it, than males, though by no means exempt. Of these, virgins and pregnant women are more particularly liable to its attacks, as well as all those who are much visited by hysterical affections, constipation, and flatulency. It is sometimes also found to accompany the chlorosis or green sickness. On the whole, however, it is of comparatively rare occurrence amongst females.

Neither is this disease very common in advanced life, unless where corpulency, or a tendency to lethargy exists. In those cases however where it does occur, it is more to be dreaded than in youth or middle age. It is no unfrequent attendant on asthmatic persons.

The opinions of medical men with respect to the immediate cause of this disease, or what by them is termed its proximate cause, have been various and discordant, as generally happens in all obscure investigations. In all probability every one of them are wrong, so that it can be of little utility to inquire into them. There is however one idea, which seems to be more universally adopted than any other, and which deserves notice; it is, that this affection is produced by a cause purely mechanical, and depending on the position of the body. Some plausible theories have been formed on this supposition, by assigning to the different thoracic and abdominal viscera, certain relative positions which would occasion a temporary pressure upon the organs of respiration, or upon some branch of the intercostal nerves. With respect to this mechanical pressure, arising from any imagined position of the patient, what I have already said on that score, renders this hypothesis vain, for there is no position in which it is possible for a person to fall asleep, in which I have not been attacked by Night-Mare. Neither is there any more dependence to be placed on the generally received opinion, of the disease being induced by a full stomach. It may naturally be supposed, that any person labouring under this affection to the degree which I have stated, although I have as yet given a very feeble idea of its extent, would take every possible precaution to keep clear of the causes, which were so generally believed to have produced it. I religiously abstained, for many years from eating any thing after dinner, and took dinner also at as early an hour as two o’clock. It was during this period that I suffered most from the disease. I think I may safely assert, that for more than twenty years, I have never once, to the best of my recollection, fallen asleep on my back, or ever found myself in that position on waking. When night after night has been rendered miserable by this enemy of repose, I have had recourse to every expedient which deep reflection could suggest. The perpendicular position of the body, I have found by experience to be the worst in which a paroxysm of Night-Mare can be borne. The difficulty of respiration, and all the other symptoms are greatly aggravated, and an additional one is felt, which greatly increases the sufferings of the patient; it is a perpetual dread of falling, which appears inevitable, and which prevents the patient from struggling so much as he would do if in a horizontal position. Next to this is the position of sleeping with the body bent forwards, and the head reclining with the face downwards on a table: in this last position, the difficulty of inflating the lungs is extreme. I have never been able to discover that any great difference arose between sleeping on the right or left side. I have always considered it as a matter of indifference. Although it is possible to render the paroxysm of Night-Mare more tolerable by any particular position of the body, yet I am well assured that no position will secure a person from its attacks, to whom it has once become habitual. I slept for some time in an easy chair, and found the disease greatly aggravated by it.

There must however be some reason for the universal opinion that it always attacks persons lying on the back. I was for a long time of opinion myself, that I was always lying in that position when the paroxysm came on, but as the disease gained strength, and the paroxysms hung more pertinaciously upon me, I became more perfectly awake, so as to be able to discover more accurately the position in which I was lying, and I found that little faith was to be given to the sensations that may occur during Night-Mare, as they are the most deceitful of all evidences. It appears to be one of the symptoms almost inseparable from the disease, that the patient should appear to himself to be kept down upon the back by some external force. This sensation I have almost always felt, even when I have had the evidence of other people, as well as my own conviction when awake, that I was in reality lying on the side. I cannot help suspecting that many others have been deceived in a similar manner, and thus made to believe, that they never had the Night-Mare except when sleeping on their backs. There is also another sensation which is very apt to deceive the patient, that is, on the paroxysm going off, and the moment of his recovering the power of volition, a great confusion of ideas always takes place, and a person to whom the Night-Mare is not very familiar, generally imagines that he has recovered himself by some effort of his own, frequently by turning from his back to his side, sometimes by sitting upright in bed. These things are all extremely fallacious; there is no trusting to the senses during a paroxysm of Incubus; nothing short of the evidence of another person ought to satisfy the patient. I have often been thoroughly convinced in my own mind that I had succeeded in throwing the bed-clothes off my breast, and by that means gained relief, and not unfrequently, that I had risen from bed, and opened the window to admit air; yet both these ideas have been proved to be incorrect. I have often felt very certain that my right arm was out of bed, and that I had moved it about; but on waking thoroughly, I have found it under the bed-clothes, and in a situation in which it could not have been moved. I cannot help thinking then, that the universal idea of its attacking persons exclusively lying on the back, is founded on an error, arising out of the ordinary sensations of the patients themselves, who have always that idea, let them be in what position they will. Several persons, subject to habitual Night-Mare, have become convinced of the truth of this observation, which I had made to them, after attending more closely to their real situation during the continuance of, and immediately after the paroxysm. I have also convinced one or two medical friends, who were extremely sceptical on that point, that it would attack me in any position, by going to sleep before them, on a chair, or sofa, when my own feelings have indicated the certainty of attack, if I should indulge for a few moments the propensity I felt to sleep.

Neither is it necessary for the stomach to be filled with food, in order to produce Night-Mare, as is evident from what I have stated above with respect to the abstinence I observed during the period in which I suffered most from this affection. Experience has taught me that I may eat heartily of some kinds of food, just before going to bed, with impunity; whilst the smallest quantity of some other will inevitably bring on the disease, in spite of all the precautions that can be taken.

Thus then we must give up every explanation of the phenomena which occur in this disease, founded upon principles purely mechanical, however plausible they may appear. Neither is the opinion of Darwin more correct, that the Night-Mare is nothing more than a consciousness of the suspension of the power of volition, and a desire to recover that power. If so, it would differ little from sleep itself; or, however fatiguing it might be to the mind, it could not occasion any derangement in the functions. The breathing and the circulation would go on without any interruption, as in sleep; nor would there be any thing that could produce the sense of oppression on the breast. Darwin was well aware of this difficulty, and therefore chose rather to contradict the generally received opinion of oppression and difficulty of respiration. There is no doubt whatever of the difficulty of breathing, which any one may assure himself of, if he could have the opportunity of seeing a patient during the paroxysm of Night-Mare. I have taken considerable pains to assure myself of this circumstance from the evidence of other persons.

I must confess I have not hitherto been able to find any satisfactory explanation of the phenomena which take place during Night-Mare. The following observations which I have been able to make on the paroxysm itself, and on the more immediate causes which give rise to it, may possibly direct some happier genius to a more correct idea of its nature.

1st. I have frequently experienced that this affection may occur in very profound sleep, without breaking or disturbing that sleep, any farther than to produce a dream, the memory of which will remain after waking, in the same manner as that of any other impressive dream. Thus I have frequently dreamed that I had Night-Mare; supposing myself to be in a place, and under circumstances very different to those in which I really was. Under these circumstances I have never become conscious of the real situation in which I was, but on waking, remembered very well that I had been dreaming of labouring under Night-Mare. From this circumstance I conclude, that the Night-Mare is not, as Dr. Darwin insinuates, a state of imperfect sleep, but an absolute disease, which may occur, and go through its regular stages, whilst the patient continues to be, to all intents and purposes, in a natural sleep. There is no doubt but the disease, in this case, is much slighter than ordinary, although the impression made upon the mind may be very strong.

2nd. It happens still more frequently, that the patient is in a state apparently between sleeping and waking, when the paroxysm takes place; which has given rise to the belief, in many persons, that it came on while awake. I have often heard it described by others, (and have felt it myself) as a sense of weight, first upon the feet, and progressively advancing towards the breast, until the paroxysm becomes complete. In the beginning of this state of things, it appears to the patient that he might easily, if he would, move himself, and shake off the incumbent weight. He does not feel at all aware at that moment, of the suspension of the power of volition; nor does he feel any inconvenience from that circumstance until he begins to experience a necessity of exerting that power, in order to carry on the function of respiration. It is not until the involuntary action of the muscles concerned in respiration, in some measure ceases, that the patient perceives that he is absolutely labouring under Night-Mare.

I have paid very close attention to this circumstance, and have been repeatedly convinced, that whenever the disease attacked in this manner, I was always asleep at the commencement of the paroxysm, and that as soon as I became conscious of my situation, or in other words, awake, the power of volition was completely suspended, although very little inconvenience arose from it; for, on making the attempt to move, which appears very easy to do, I have always felt the paroxysm of Night-Mare to be completely formed, and the difficulty of respiration, which before did not exist, immediately to come on, and with it all the anxiety and distress which characterize this disease.

From this I infer, that a suspension of volition always exists during a paroxysm of Incubus, but that this is not alone sufficient to constitute a complete Night-Mare, even when attended with a consciousness of our situation. It is likewise necessary that the involuntary action of the respiratory organs should experience some interruption, and I am disposed to think that the circulation through the lungs, and the action of the heart itself, partakes of this interruption. I conceive also, that the difficulty of inflating the lungs is always increased in proportion as the patient becomes more awake.

3d. It has almost constantly occurred to me, especially since the disease had gained such considerable strength, that the power of volition has been partially recovered for some time before the paroxysm ceases. I have always recovered this power, first in the lower extremities, and last of all in the head. It begins first to return in one or both feet, and by moving them about as well as circumstances will allow, I recover by degrees the command over the muscles of the legs and thighs, and afterwards of the arms, but partially, and not without great exertion, which exhausts me much, and does little good towards shaking off the paroxysm. I have however at sea frequently profited by this power, for I have been able to communicate a considerable motion to the cot in which I slept, by pushing against the foot of it with one of my feet, until it swung so much as to touch against something, and by that means produce a shock, which being external, has frequently dispelled the fit. It is really surprizing how slight an impression from without is sufficient sometimes to recover the patient. Although I have frequently rolled about the bed, and kicked all the bed-clothes off from me, I have not been able to succeed for a long time in recovering myself from the paroxysm, when it has instantly disappeared on receiving a moderate shock from another person, or even by any one taking hold of my hand.

It is only however in the advanced stage of the disease, that this severe struggle takes place. In the general way the patient is instantly liberated from the paroxysm, as soon as he can succeed in moving any of his limbs. I have seldom met with any one who was able to articulate during the paroxysm, though I have generally been able myself to call any person by name, who might be near me, and to beg of them to wake me, but this is always effected with difficulty, and only after the paroxysm has already continued some time.

4th. It frequently happens, especially when a person is anxious about rising at a particular hour, and afraid of over-sleeping it, that he becomes conscious of that circumstance in his sleep, and feels an ardent desire to wake himself; to many persons this is by no means a difficult task, and is soon accomplished; but to those who are subject to Night-Mare, the reverse of this takes place. They strive with all their might to awake, and soon become conscious of their precise circumstances, but cannot recover the power of volition; after contending for this a short time, the breathing at length becomes laborious, and a complete paroxysm of Night-Mare succeeds, which always is severe in proportion as the patient happens to be more perfectly awake.

From these observations it results, that the nature of Incubus is essentially different to that of either sleeping or waking, and is an absolute state of disease which may occur during sleep in a slight degree, without breaking that sleep; that it consists in a suspension of the power of volition very different to what takes place in natural sleep, because it is accompanied with a consciousness of that suspension, and a strong desire of recovering this power. But neither is this sufficient to constitute Night-Mare, although this disease will, I believe always, result from such a state of things, yet the paroxysm is by no means complete, until, in addition to the general paralysis of all the muscles of voluntary motion, there shall occur likewise a partial paralysis of some of those concerned in the functions, which are performed independently of the will, especially of respiration and the circulation of the blood, the consequence of which will be a difficulty of breathing, with a sense of oppression about the præcordia, and fluttering of the heart. I conceive these symptoms to arise principally from a temporary paralysis of the nerves of the diaphragm; or rather an inaptitude in those nerves, together with some others of the principal branches of the intercostals, to perform their functions. Thus then, from this partial paralysis of the diaphragm and thoracic muscles, the patient is rendered incapable of dilating the chest so as to allow of the expansion and consequent inflation of the lungs; the blood consequently meets with some interruption in its passage through that organ, and this interruption is speedily communicated to the heart; the re-action which takes place here is quickly communicated to the whole system, and probably is the principal cause of the final solution of the paroxysm. How this solution is at length effected is, I confess, a difficult and obscure question. There are two ways in which it takes place; the first and most frequent is by the patient becoming perfectly awake, by which means he recovers at once the power of volition, and the partial paralysis of the diaphragm and thoracic muscles at the same moment ceases, these muscles being then moved by the power of the will. The other mode by which a solution of the paroxysm is effected, is by the patient falling into a more perfect sleep, and losing that consciousness which accompanies Night-Mare. The involuntary actions then go on as before without interruption, and if the dreams continue, they are no longer of that harassing and distressing kind, but are now natural and easy. It is not only in slight cases of Incubus that the patient recovers from the disease without waking, but sometimes I have known it to happen even in very severe paroxysms, where I have become conscious of the place and situation in which I was, and yet have instantly been asleep on the cessation of the paroxysm. There appears to me a greater difficulty in explaining this mode of the solution of the paroxysm than the other, as there seems no evident cause for the cessation of the paralysis of the Diaphragm, &c. Every thing connected with the phenomena of sleep, is extremely obscure; and nothing on this subject appears to me more extraordinary, than the sudden transition from the sleeping to the waking state. Whatever it is which takes place at that moment in the brain, and in the whole system, takes place only partially during Night-Mare. Is it very absurd to suppose that a part of the system may recover the waking state, while the brain, or some other part, remains asleep, for want of a sufficient stimulus to rouse them? I cannot help thinking but something very similar to this takes place in Night-Mare: hence the power of moving the lower extremities, whilst the superior ones remain paralyzed: hence the little good resulting to the patient from his own struggling, whilst a comparatively slight touch from another person is sufficient to dispel the charm. Hence the appearance of visions, whilst in every respect the patient appears to himself to be perfectly awake. It seems that the brain continues to present a succession of images to the mind as in sleep, whilst at the same time, the body is become susceptible of external impressions, and conscious of internal ones, such as those arising from the derangement which has taken place in the functions of the heart and lungs.