Sleep Paralysis: You're Awake, But You Can't Move [View all]

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http://www.huffingtonpost.com/dr-michael-j-breus/what-is-sleep-paralysis-_b_7131030.html

Have you ever suffered an episode of sleep paralysis? It can be a tremendously frightening experience, one you're not likely to forget. You wake from sleep immobilized, unable to move your body or turn your head. You try to make a sound, but you can't open your mouth. You feel short of breath, with a strong feeling of pressure on your chest, weighing your body down. You feel a deep sense of dread or danger -- maybe you even feel there's a strange presence in the room.

As frightening as it is, sleep paralysis -- one form of parasomnia -- isn't actually dangerous, nor is it typically a sign of a serious condition. Sleep paralysis is one symptom of narcolepsy, but many instances of sleep paralysis aren't an indication of narcolepsy or another sleep disorder. Episodes of sleep paralysis can last for a few seconds or as long as a few minutes. Sleep paralysis can occur when you are awakened from sleep, and it also can occur when you're in the process of falling asleep. What's behind this difficult sleep experience? The cause of sleep paralysis isn't known. But it appears likely that many instances of sleep paralysis occur because of difficulty transitioning between different sleep stages, particularly moving in and out of REM sleep.

During REM, the body goes into a state of paralysis known as REM atonia. This is a normal part of the sleep stage, when major muscle groups and most voluntary muscles are paralyzed. One important function of this paralysis may be to protect the body from injury during sleep. REM is a sleep stage when much active dreaming occurs. Without the paralyzing effects of REM atonia, we might act out physically in response to our dreams. In certain sleep disorders, including REM Behavior Disorder, the normal paralysis of REM sleep doesn't work as it should, and people act out physically -- sometimes aggressively and violently -- in sleep.