Why We Sleep

Amazon

This book does not mess around. It gets right to the point:

While we begin our sleep with a prolonged NREM state, the later half of our rest has more REM sleep or dreaming opportunities.  Our NREM sleep time is spent sorting our unneeded neural connections and REM comes in later to strengthen the remaining connections.

You probably know about REM and NREM sleep already. But if you don't, you can get this free book easily. And download it to the Kindle PC reader.

This shows why we die, if we cannot sleep. Our brain stops working!