Notes about what happens when you sleep

An article on ScienceLine.com discusses What Happens to Your Body When You Fall Asleep.

The post notes "There is no universally agreed-upon definition because falling asleep is not a split-second occurrence, not an abrupt switch from awake to asleep. Rather, it is a gradual progression of stages in which body and brain activity changes."

If you're wanting a brief overview of sleep, this is a useful and quick read that discusses the various stages of sleep.