Sleep paralysis occurs in up to 8% of the population.
Clinical features of sleep paralysis:
(1) It occurs at sleep onset or upon awakening.
(2) It involves inhibition of voluntary muscle movements for seconds or minutes.
(3) Sensory perception of the immediate environment is preserved.
(4) It may be associated with fear, distress or sense of doom.
(5) It may be associated with nightmares or dreams.
It may occur by itself ("isolated") or associated with other sleep disorders such as narcolepsy.
