Somnambulism (Lat. somnus, 'sleep,' ambulo, 'I walk') is a disorder of sleep. It is symptomatic of more or less activity in some of the psychical and motor areas of the brain, while the centres that preside over consciousness are slumbering soundly. There are different forms, as sleep-crying, sleep-talking (somniloquy), and sleep-walking. These all involve sensori-motor acts.
Sleep-walking is closely related to hysteria and epilepsy, and it occasionally alternates with these and allied diseases. It occurs mostly in youth, affecting males and females in almost equal proportion; commonly, although not invariably, it disappears when adult age is attained. It is met with chiefly in persons of nervous temperament, and in those who have an inherited proclivity to neurotic disease. The exciting causes embrace mental excitement, overwork, fright, bodily fatigue, hepatic and digestive disorders, worms, and an overloaded bladder, and in females uterine and ovarian troubles. Sleep-walking is one of the neuroses of deep sleep. It occasionally presages graver maladies; generally these may be prevented by suitable treatment. It is important to recognise that it is a pathological state, and that no one who is in perfect health walks in his sleep. Sleep-walking is an acted dream, which generally supervenes when sleep is deepest—often during the first deep sleep. The dreamer usually stages it so precisely that he is able to act it with admirable exactness. In the first visitation the dream may be simple, and merely impel the sleeper to rise from bed to walk round the room and then return to bed. Eventually the dreams become more elaborate, and may embrace many complex operations, in which the individual has to elude articles of furniture, unlock doors, open windows, walk along dangerous roofs, or beside the edge of precipices—in short, perform feats he could not possibly execute in his waking moments.
Sleep-walkers have achieved the most diverse exploits without awaking. They have swum across rivers, thrashed corn, ridden on horseback, and even transacted their usual daily work. They are oblivious to danger, and untrammelled by fear; this, combined with an exaltation of muscular sense, enables them to effect their movements precisely and quickly. Their feats, however, are sub-conscious, and not, as it is popularly supposed, superhuman. Their senses, which are not connected with the dream, slumber; they do not see, hear, or smell, so they perform with their eyes shut as well as open, and they may be shaken, and may themselves cough and sneeze without being awakened. A certain degree of anaesthesia appears to render them insensitive to pain. After the dream-act is ended the sleeper returns to bed, to sleep until the usual hour for rising, and when he awakes he either does not recollect anything about his escapade, or remembers it only as a dream. Most frequently he recollects it in a subsequent sleep-walk, just as some dreams are only remembered in recurring dreams. Sleep-walking leads the actor into situations which endanger life, and annually many deaths are recorded from fatalities so arising. If the sleep-walker be awakened at a critical moment, coolness and precision are replaced by agitation and fright, and movements become halting and clumsy, and accident usually follows. Many tragedies have been enacted in this state, and these are of great forensic interest. From every point of view sleep-walking is a source of much anxiety to the afflicted and his relatives.
A sleep-walker found in his wanderings ought not to be awakened, but led back to bed as gently as possible. Abrupt awakening may give rise to shock, and may mark the onset of grave nervous disorders. Whilst it is always advisable to seek medical advice, it may be indicated that the general health should be attended to, so that it may be improved; and all exciting causes should be remedied or avoided, as, for example, all undue excitement and fatigue of mind and body. The sleeping conditions require consideration; in some cases it is advisable that some one should sleep in the same room. Occasionally, it is advantageous to awaken the sleeper at the end of the first hour of sleep, when it is deepest, to prevent it becoming too profound. Hypnotism is sometimes called artificial somnambulism. See the works and articles cited at SLEEP.