The nature of sleep.

Normal human sleep is often described as a state of reduced activity and reactivity, a kind of low general vigilance. Despite decades of intense scrutiny, our understanding of natural sleep is still incomplete. The two fundamental stages of sleep, nonrapid eye movement (NREM) and rapid eye movement (REM), are present in man as well as animals. Problems with sleep are frequent complaints of modern man, and a variety of these complaints are explored. Cognizance of the essence of normal human sleep may facilitate the anesthetist's understanding of pharmacologically induced sleep.