Why Is REM Sleep Also Called Paradoxical Sleep?

REM sleep is also called paradoxical sleep because in this state, the sleeper is difficult to wake-up in spite of showing the brain waves associated with waking, hence the term paradoxical, as the state itself is somewhat contradictory. Dreaming occurs during REM sleep.

REM stands for rapid eye movement, which is the main characteristic of the sleep state; REM occurs roughly every 90 minutes, and although much is still unknown about REM, it is vital for human function. During REM, sleepers will experience sleep paralysis, dreams and EEG brain waves, which indicate waking even though the sleeper is unlikely to wake during this time.