Definition reprinted with permission from Culebras, Antonio Butterworth-Heinemann:[amazon 0750696443 inline]
Desynchronized sleep, characterized by enhanced brain metabolism and vivid hallucinatory imagery or dreaming. There are spontaneous rapid eye movements, resting muscle activity is suppressed, and awakening threshold to insignificant stimuli is high. The EEG is a low voltage, mixed-frequency, non-alpha record. REM sleep is usually 20-25% of total sleep time. It is also called "paradoxical sleep."