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This sleep stage is known as the rapid eye movement stage because the eyes quickly move back and forth behind the eyelids during REM sleep. Rapid eye movement sleep differs so much from other sleep stages that other sleep stages are collectively referred to as non-REM sleep.People with healthy sleeping patterns cycle through these five stages of sleep several times each night. As a person continues cycling through the sleep stages during the night, the REM sleep stages last longer and longer with each cycle. For instance, while the first REM stage lasts approximately ten minutes, the last period of REM sleep can last up to an hour.One theory suggests that REM sleep helps people consolidate memories and learning. In fact, studies indicate that REM sleep improves memory recall. However, it's also true that loss of REM sleep has no observable negative affects on memory.