Sleep Disorder Sleep normal physiology  Nearly one third of human life is spent in sleep.Sleep which is broadly divided into two broadly different phases 1.REM-sleep (rapid eye movement sleep) 2.NREM-sleep (non-REM sleep) In an 8 hour sleep, usually 6-6½ hours are spent in the NREM-sleep while 1½-2 hours are in the REM-sleep. The REM-sleep occurs