What happens when we sleep?

We have daily rhythms of waking and sleeping called Circadian rhythms.  While we sleep there are distinct phases of sleep which repeat in a cycle/pattern every 100 minutes, so we may pass through these phases a number of times each night depending on how long we sleep.

Sleep is an active process and during each of these phases there is a complex exchange of hormones and chemical messengers affecting our nervous systems.   Brilliant sleep requires this to be a balanced system. The best sleep happens when all these phases occur naturally - if they are broken/interrupted the quality of sleep may be affected.