What happens when you sleep

What happens when you sleep? Is it like being half way dead and half way alive? I need to know please be very detailed. Thanks

While many of us think of sleep as a largely forgotten stretch of time when nothing happens, sleep is, neurologically speaking at least, a busy time indeed. Although sleep's importance is inarguable, scientists do not know exactly why it is so important to our survival. What happens when we sleep?

Sleep Stages

Scientists recognize sleep stages by tracking the changes in brain waves. The five sleep stages are repeated as many as five times during the night. As the night progresses, each cycle lengthens, and REM sleep, during which most dreaming takes place, extends.

Sleep Stage 1

In this brief stage, which may last only a few minutes, the body drifts to sleep. Brain waves are mostly high amplitude, slow waves and occasional alpha waves (like those found when awake).

Percent of total sleep time for young adults: 5 percent.

Sleep Stage 2

Heartbeat and breathing slow and the sleep is deeper than in Stage 1. Slow-wave sleep continues with peaks of brain waves (known as sleep spindles) occurring.

Percent of total sleep time for young adults: 44 to 55 percent.

Sleep Stages 3 and 4

These are the stages of deepest sleep, when brain waves are slowest. During these stages breathing and heartbeat slow further and muscles relax. Dreams are more common than in the earlier stages and sleepwalking and talking may occur during Stages 3 and 4.