A common condition characterized by transient partial or total
paralysis of skeletal
muscles and areflexia that occurs upon awakening from
sleep or less often while falling asleep. Stimuli such as
touch or
sound may terminate the episode, which usually has a duration of seconds to minutes. This condition may occur in normal subjects or be associated with
narcolepsy;
cataplexy; and hypnagogic
hallucinations. The pathophysiology of this condition is closely related to the normal hypotonia that occur during REM
sleep. (From Adv Neurol 1995;67:245-271)