When this is over, the cycle starts over; the original star dies and becomes a white dwarf. White Dwarf The core of a white dwarf star surrounds itself with layers of hydrogen, which still burn, continuing to fuse.
REM sleep is important because it is the restorative part of our sleep cycle. Typically, you begin the sleep cycle with a period of non-REM sleep followed by a very short period of REM sleep. The period of non-REM sleep is made up of stages 1 to 4. Each stage can last from 5 to 15 minutes.
Following the N3 stage of sleep, a series of body movements usually signals an ascent to lighter NREM sleep stages. Typically, a 5- to 10-minute period of N2 precedes the initial REM sleep episode. REM sleep comprises about 20 to 25 percent of total sleep in typical healthy adults. NREM sleep and REM sleep continue to alternate through the night in a cyclical fashion. Most slow-wave NREM sleep occurs in the first part of the night; REM sleep episodes, the first of which may last only one to five minutes, generally become longer through the night.