In the popular mind posture in sleep and indigestion are regarded as the chief causes of nightmare. Generally a person who has nightmare awakens to find himself sleeping on his back, and thus sleeping on the back has become regarded as a cause. That this sleep posture may be provocation of attacks is certain; it is possible, however, for attacks to occur no matter what the sleep posture; practically identical attacks may take place when the person sleeps in the upright posture, even when awake. The usual reason given to explain why sleeping on the back predisposes to nightmare is that such a position allows the abdominal organs to press upon the large blood vessels of the abdomen, thus interfering with the flow of blood to and from the brain and other organs.

Dyspepsia is by far the most commonly accepted explanation, just as it is the wont of most people to attribute all bad dreams to digestive disturbances. That these errors may play a part is true. Probably many of us are aware of the unquiet dreams to which heavy or late dinners may give rise. While many dyspeptics suffer from restless sleep, there are a great many other persons whose digestions are very good who are more or less subject to anxiety dreams. When indigestion is considered a cause of nightmare it is supposed to operate by distending the stomach, this in turn pressing upon the diaphragm, lungs, and heart..

Other physical disturbances, as constipation, eye defects, heart and kidney diseases, etc., are listed as etiologic factors. If these operate they can do so only by the impression they make upon the brain. We may assume that nightmare is due to some profound impression made on the brain by some physical error, but if we do so we are then at a loss to explain why nightmare should occur in persons who, as far as can be determined, are in good physical health. Being conservative, we must admit, therefore, that two factors are operative in promoting the disorder, namely, physical and . mental.

The mental causes of nightmare are many and varied. Possibly the dream may concern itself with some terrifying experience or other unhappy incident that actually happened to the individual. Sometimes ghost, murder, and other stories, especially when told or read near bed time, may instigate a terrifying dream, particularly in persons of an impressionable temperament. In some instances, even in adults, terrifying dreams can be traced to fairy stories told or read in childhood. The fear would be caused by the apparent actuality of the dream for; as before stated, dreams appear to be very real, no matter how absurd they may be. to waking reason. The palpitation of the heart and disturbed respirations can be traced to the effects, of the emotions on the physical structures; and the paralysis, or sense of helplessness, to an awakening of the sensory centres prior to that of the motor centres.

Not infrequently the attack is due to the dream's bringing to a realization a wish or fear that has been repressed by waking consciousness. The wish or fear may be strong, so much so that it causes a conflict in the mind of the individual. We may define a mental conflict as a lack of harmony between two or more elements of mental life, a sort of antagonism between two ideas. To take a simple example, let us suppose that a person desires the good things of the world so much that a temptation to steal is evolved. This temptation could not be yielded to, at least not by a person of integrity. The temptation is, therefore, pushed back from consciousness, repressed; it will not be tolerated in consciousness. However, the desire is strong, likewise the forces opposing its gratification, producing an unrest which disturbs the individual. For one reason or another, a dream is instigated in which the person seems to steal and, conscious of the impropriety of the act, he is greatly troubled.

Mental conflicts may be concerned with many things, in fact with any strong desire which the individual opposes. If the opposed desire meets with fulfilment in a dream, it will usually cause distress. Some writers trace nightmare to erotic sources. In such cases we may conceive that some physical stimulus or other cause promotes a dream in which erotic thoughts, wishes or fears, appear to be in danger of fulfilment, the distress being caused because sleeping consciousness recognizes the nature of the dream and antagonizes it. If we look upon nightmare as due to many causes, as childhood experiences, unpleasant incidents in later life, mental conflicts of one kind or another we will be covering its etiology without bias.

A point which causes some individuals thought is why they should experience so much concern in dreams over

•incidents which in waking life would not trouble them in the least. Often the things that frighten in the dream are, judged by waking reason, very insignificant. Various reasons might be given; for example, we might say that in dreams the reasoning powers available to waking life are absent or feeble. But in many instances the reason is that sleeping consciousness rightly interprets the significance of the dream, and the thoughts on which it is built. In other words, sleeping consciousness understands the symbolism of the dream. When one awakens there is a transition to another consciousness which does not, or does not want to comprehend the significance of the dream. Further, if, in attempting to ascertain the thoughts underlying the dream, we asked the person to tell all the ideas that came to his mind in association with the various elements of the dream, we would find, after a time, a reluctance on his part to continue. This would be because the individual does not wish to reveal the dream thoughts, since they are opposed to his nature, or they cause disquiet in other ways. This reluctance is technically known as resistance, and is not uncommon when one tries to explore the mental realm.

It may be asked why more people are not subject to nightmare, considering how impossible it is not to have had an unpleasant experience, or desires or fears which must be repressed. We may attribute this to the fact that it is only when the repressed thoughts are very strong that nightmare is apt to be frequent; being of a strong emotional tone, they are easily awakened by slight physical or other stimuli, or they may easily force their way into sleeping consciousness when sleep slackens the repressing powers of the waking state. Occasional attacks may be due to physical stimuli promoting a dream somewhat similar to the nature of the stimulus, or the dream may, by association, awaken a terrifying experience, if only an imaginary one. Some individuals are susceptible to disturbing dreams just as certain people are susceptible to particular physical ills. We should not think that it is only nervous persons who are subject to nightmare, though, probably, these are more predisposed than others because of their emotional life. Nightmare may happen to any one; should it become habitual it is best considered as evidence of some powerful idea or experience in need of removal.