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.
These are called rapid eye movement (REM) sleep, and non-rapid eye movement (Non-REM) sleep. In adults, non-REM sleep occupies around 80 percent of the night, and REM sleep 20 percent. However, REM sleep does not occur in one large block. Actually, we go into REM sleep in cycles of around 90 minutes. That is, REM sleep occurs around once every 90 minutes.