Scientists know a great deal about sleep these days, even though much is still a mystery. What we can say for sure is that how many hours we sleep is not as important as we might think. Rather, it is the ‘restfulness’ that counts. In other words, quality over quantity. Restful sleep means deep sleep, in which your body functions are at a minimum and your brain is showing little activity. It is a deep, dreamless state that can be likened to being at the bottom of an ocean. Scientists call it the NREM phase. Then there is the REM phase where your body is active and your dreams vivid. We could compare this phase to being on the bright shallow coral reeves. Your body is very active - REM stands for rapid eye movement as your eyes are constantly moving. Mumbling in your sleep is also common.