The brain is our most metabolically active organ and it has a waste removal system all of its own.
While we and our brains are awake and active, we accumulate metabolic waste within the interstitial spaces between cells.
When we are asleep the volume of interstitial space expands allowing more fluid to flow through to clear out the waste.
This means that when we sleep, we are literally cleaning up our brains of the waste and rubbish accumulated through the day.
No wonder we need so many hours of sleep!
6-7 hours is a healthy nightly amount