What happens when we sleep?

What happens when we sleep? 

Sleep is a mysterious state which is both more active and complex than it first appears.

Not all sleep is the same. The Sleep cycle shows the different types or stages we go through as we sleep:

Read a description of the Sleep cycle diagram

We will move through these different types of sleep – 4 or 5 times – through the night and may wake up briefly as well. Having a good night’s sleep depends on spending enough time in deep sleep (Non-REM stage 3). When you have had enough deep sleep you will wake up feeling refreshed and full of energy.