Dissociated states of wakefulness and sleep.

Both sleep clinicians and basic science researchers have been witness to a wide variety of unusual clinical and experimental phenomena that represent admixtures, incomplete declaration, or rapid oscillations of the three states of being: wakefulness, rapid eye movement (REM) sleep, and nonrapid eye movement sleep. The concept of state dissociation provides an explanation for a wide variety of bizarre clinical phenomena, including the symptoms of narcolepsy, REM sleep behavior disorder, disorders of arousal (such as sleep terrors, sleepwalking, and sleep drunkenness), automatic behavior, and some "out-of-body" experiences. The purpose of this review is to provide an overview and perspective of such conditions, encourage systematic and detailed study of these "experiments in nature," and underscore the interdependence of clinicians and researchers.