Have you ever woke up but been unable to move? Sleep paralysis is paralysis associated with sleep that may occur in healthy persons or may be associated with narcolepsy, cataplexy, and hypnagogic hallucinations. Sleep paralysis occurs either when falling asleep, or when awakening. 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. Physiologically, sleep paralysis is closely related to REM atonia, the paralysis that occurs as a natural part of REM sleep.