<p>REM sleep begins 60-90 minutes after sleep onset. During REM sleep we lose muscle tone, except for eye movements. Respiration and heartbeat may become irregular.&nbsp;</p><p>During REM sleep, small muscle movements (phasic twitches), are seen in the face and extremities. Saccadic eye movements accompany REM sleep, which can be seen under the person's closed eyelids. The EEG in REM sleep is of low voltage, with a mixture of rhythms. It may look very much the same as the EEG during wakefulness with eyes open, except for the lack of EMG contamination.</p><p>If REM sleep that begins less than one hour after sleep onset, it is called REM onset sleep. This can be an abnormal finding indicating a sleep disorder called narcolepsy if accompanied by other symptoms and repeatedly demonstrated.</p>