Over the past few decades, researchers have learned that the quality of one's sleep has a great deal to do with overall health. Once thought that the brain was dormant while sleeping, it is now known that the brain is very active, especially during REM sleep.
REM is an acronym for rapid eye movement. This is one of 5 stages of normal sleep patterns. Leading up to REM sleep are four stages, each lasting anywhere from 5 - 15 minutes.