Sleep Paralysis (cont.)

Sleep paralysis usually occurs at one of two times. If it occurs while you are falling asleep, it's called hypnagogic or predormital sleep paralysis. If it happens as you are waking up, it's called hypnopompic or postdormital sleep paralysis.

As you fall asleep, your body slowly relaxes. Usually you become less aware, so you do not notice the change. However, if you remain or become aware while falling asleep, you may notice that you cannot move or speak.

During sleep, your body alternates between REM (rapid eye movement) and NREM (non-rapid eye movement) sleep. One cycle of REM and NREM sleep lasts about 90 minutes. NREM sleep occurs first and takes up to 75% of your overall sleep time. During NREM sleep, your body relaxes and restores itself. At the end of NREM, your sleep shifts to REM. Your eyes move quickly and dreams occur, but the rest of your body remains very relaxed. Your muscles are "turned off" during REM sleep. If you become aware before the REM cycle has finished, you may notice that you cannot move or speak.

Up to as many as four out of every 10 people may have sleep paralysis. This common condition is often first noticed in the teen years. But men and women of any age can have it. Sleep paralysis may run in families. Other factors that may be linked to sleep paralysis include:

• a lack of sleep
• a sleep schedule that changes
• mental conditions such as stress or bipolar disorder
• sleeping on the back
• other sleep problems such as narcolepsy or nighttime leg cramps
• use of certain medications
• substance abuse

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Source: MedicineNet.com
http://www.medicinenet.com/sleep_paralysis/article.htm