All parts of the body, which are the seats of active change, require regular periods of rest. In the case of the brain, it would be impossible that there should be only short periods of activity and repose, that is, of consciousness and unconsciousness. Hence the necessity for regular periods of sleep.

Sleep is a condition that is a remarkably perfect example of what occurs at varying intervals in every working portion of our bodies. Sleep, therefore, affords the body the interval during which energy that is expended during the day is renewed.

The influences of personal habits, ago, temperament and occupation have much to do with the duration and quality of sleep in different individuals. Years ago it believed that sleep without dreams was best. The thinking was that dreaming meant the sleeper was not in a deep sleep and would be prone to sudden waking. Today, many medical professionals believe that we need periods of rapid eye movement sleep or REM sleep, which is the period during which we dream.

Among sleep disorders, sleepwalking is one of the most curious. Somnambulism is a state where, while sleeping, a person moves and acts as though conscious. Walking during sleep is the most common manifestation of somnambulism. The sleeper may perform many apparently voluntary actions. The sleeper may perform all manner of different tasks, and to the casual observer may seem completely alert and awake.

The sleeper may get out of bed, get dressed, go outdoors, and perform other tasks. In some cases the sleeper may carry engage in conversation. On waking in the morning the subject may have absolutely no memory of the event or may feel the experience was a dream. Early explanations of sleepwalking included some very bizarre theories, including demonic possession or other paranormal phenomenon.

A myth that continues to this day is that waking a sleepwalker is dangerous. Given that the subject is not awake, it may in fact be more dangerous not to wake them. Later research has concluded that somnambulism can be successfully treated.

Shakespeare understood all to well that dreams are more than mere trains of ideas, which present themselves to the mind during sleep. In dreaming there is no voluntary control of the current of thought and the principle of suggestion has unlimited sway. Usually there is no coherence in the images that appear, but the most extraordinary contradictions excite no surprise in the dreamer.

Occasionally however, intellectual efforts are made during sleep that would be difficult to surpass in a waking state. It is said that Coleridge composed Kubla Khan, a beautiful fragment of a poem, while he was asleep. It is said that that similar occurrences have been recorded by other people.

Dreams arise from very natural causes and are merely the result of mental processes stimulated in the same way as are out thoughts during the daytime. A sensation of cold may cause one to dream of snowstorms and freezing while a ray of light may incite one to dream of a fire. It was said that a case of indigestion or eating a heavy meal too late at night might have brought on nightmarish dreams.

Years ago it was thought that dreams may in a general way indicate the condition of a persons health or mental wellbeing and was the frequent accompaniment of some forms of disease.