Sleep paralysis is classified within the rapid eye movement (REM) sleep parasomnias as a transient sleep/wake phenomenon occurring when entering into or awakening from REM sleep, with elements of REM sleep persisting into wakefulness. In particular, the REM sleep-associated muscle atonia seems to persist in an awake brain, leading to the often distressing experience of being incapable to move. Several historical descriptions and iconic representations delineate a picture of a conscious brain in a 'sleeping' body. The electroencephalography (EEG), electrooculography (EOG) and electromyography (EMG) features (awake, asleep, or admixture of both stages) during sleep paralysis
have been challenging to document, as it is difficult to capture this brief and unpredictable experience in a sleep laboratory.
However, some rare sleep paralyses have been documented during polysomnography in healthy participants and in patients with narcolepsy. In healthy participants, only episodes elicited by forced awakenings have been studied, using a sleep–wake
schedule known to facilitate sleep onset REM periods (SOR-EMPs).
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