When it occurs upon falling asleep, the person remains aware while the body shuts down for REM sleep, and it is called hypnagogic or predormital sleep paralysis. When it occurs
upon awakening, the person becomes aware before the REM cycle is complete, and it is called hypnopompic or postdormital. The paralysis can last from several seconds to several minutes, with some rare cases being hours, "by which the individual may experience panic symptoms" (described below).