Sleep

Small or subtle interruptions in a persons' waking moments of discernment are not usually noted; but the interruption called sleep is made categorically distinct because of its obvious physiological characteristics. In fact, sleep is a variety of levels of consciousness (or lack of consciousness) in which the normal individual spends between one quarter and one third of his life. Although there is awareness of having slept there is no actual awareness of the sleeping state except in the case of dreams, which may be wholly, partially, permanently or temporarily remembered or not remembered at all (although the dreaming state may be known to have occurred due to external observation of the sleeper). On first falling asleep the individual enters orthodox sleep, a physiological and psychological continuum with wakefulness where no obviously abrupt change in consciousness occurs. This is followed by paradoxical sleep, where changes are abrupt and discontinuous. The stages of sleep have also been described in terms of rapid eye movement, electroencephalogram readings and other physical measurements. There is a cycle from 1 to 4, shown by increasing delta wave activity, then from 4 to 1, which is marked by rapid eye movements and dreaming. The cycle repeats several times each night, gradually spending less time in stages three and four and more time dreaming.

There may be changes in consciousness, but sleep does not involve complete absence of consciousness. There is some monitoring, so that the passage of time is usually estimated quite accurately. An individual can often awaken at a predetermined hour, or just before the ringing of an alarm clock. Again, the individual will respond to loud or unexpected noises or to the speaking of his own name. A mother may waken at the first slight noise made by her baby, although ignoring other, much louder noises.

Although little is known of the function of sleep, sleep deprivation has marked effects, ranging from irritability and headache through blurred vision and hallucination, disorders in thinking and finally psychosis and depersonalization. Deprivation of dreaming sleep is particularly distressing, and sleep following a period of deprivation is particularly dream-full.

If the purely cognitive aspect of sleep is singled out, it is not necessarily in a class by itself, but rather draws attention to daytime, waking "sleep" conditions of restricted awareness, ranging from mild to severe and varying in duration and periodicity. This is not easily demonstrable, but other conditions showing that sleep is a state of varying intensity are sleep walking, hypnosis, "light" hypnosis or suggestibility, twilight sleep, and reveries. All conditions in which the potential of the individual's full consciousness is dormant, are attended by some degrees of ignorance (due to restriction of field of awareness), suggestibility or impotent will, and psychic vulnerability. Sleep is a metaphoric but partly accurate description of states of dormancy.