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.
REM sleep is an active mind inside a paralyzed body, while nREM sleep is a resting mind inside a functioning body. This is why sleepwalking is possible during nREM sleep and not during REM sleep: your body is paralyzed during REM sleep but not in nREM. As for why sleepwalking occurs... well, we still don't really know. See Wikipedia: Sleepwalking for much of the current knowledge.