I have no personal experience of the sensation of falling in normal dreaming, although Jewell and Hutchinson have found that it is more common than flying, the latter regarding it, indeed, as the most common kind of dream, the dream of flying coming next in frequency. A friend who has no dreams of flying, but has experienced dreams of falling from his earliest years, tells me that they are always associated with feelings of terror. This suggests an organic cause, and the fact that the sensation of falling may occur in epileptic fits during sleep,[118] seems further to suggest the presence of circulatory and nervous disturbance. It would seem probable that while the same two factors--respiratory and tactile--are operative in both types of dream, they are not of equal force in each. In the dream of flying, respiratory activity is excited, and in response to excitation it works at a high level adequate to the needs of the organism. In the dream of falling it may be that respiratory activity is depressed, while concomitantly, perhaps, the anaesthetic state of the skin is increased. In the first state the abnormal activity of respiration triumphs in consciousness over the accompanying dulness of tactile sensation; in the second state the respiratory breathlessness is less influential than a numbness of the skin unconscious of any external pressure. This difference is rendered possible by the fact that in dreams of flying we are not usually far from the earth, and seem able to touch it lightly at intervals; that is to say that tactile sensitiveness is impaired, but is not entirely absent as it is in a dream of falling.[119] In my own experience the sensation of falling only occurs in illness or under the influence of drugs, sometimes when sleep seems incomplete, and it is an unpleasant, though not terrifying, sensation. I once experienced it in the most marked and persistent manner after taking a large dose of chlorodyne to subdue pain. Under such circumstances the sensation is probably due to the fact that the morphia in chlorodyne both weakens respiratory action and produces anaesthesia of the peripheral nerves, so that the skin becomes abnormally insensitive to the contact and pressure of the bed, and the sensation of descent is necessarily aroused.[120] It is possible that persons liable to the dream of falling are predisposed to a stage of sleep unconsciousness, in which cutaneous insensibility is marked. It is also possible that there is a contributory element of slight cardiac or respiratory disturbance.[121]