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Sleep paralysis is a normal part of the REM sleep. However, it is considered to be a disorder when it occurs outside of REM sleep. It can occur in otherwise healthy people, as well as in those presenting symptoms of narcolepsy, cataplexy and hypnagogic hallucinations. When it occurs without narcolepsy, it is classified at Isolated Sleep Paralysis (ISP).
As discussed in the REM behavior disorder section, muscle atonia, or sleep paralysis most commonly occurs when a person is either falling asleep awakening. If an individual has awareness as the body enters or exits REM sleep, they may experience sleep paralysis. Sleep paralysis can last from several seconds to several minutes; episodes of longer duration are typically disconcerting and may even provoke a panic response. The paralysis may be accompanied by rather vivid hallucinations, which most people will attribute to being parts of dreams.
Sleep paralysis can occur in otherwise normal sleepers, and is surprisingly common in its occurrence and universality. It has also been linked to certain conditions such as increased stress, excessive alcohol consumption, sleep deprivation, and narcolepsy.
Treatment of Sleep Paralysis is often limited to education about sleep phases and atonia that normally occurs as people sleep. If episodes persist, the sleep specialist may evaluate for narcolepsy, which is commonly present in those suffering from sleep paralysis.