Why do we awaken from sleep?

Everybody has strange experiences with sleep. Sometimes we can't wait to go to sleep and other times we just can't seem to get to sleep. What is actually wake us up is something that scientists find hard to and seeing and feeling and carrying on mental activities of all sorts, we use up a lot of energy. So the brain and other nerve centers need a rest.

Sleep clears away our tiredness and when we wake up we feel rested. The most probable reason is that while we are asleep our body still feels hungry, cold or even damp, or we may experience an emotion such as fear. These feelings stimulate our brain and cause us to wake up. Of course we may wake up simply because we have had enough sleep!

Fact:
Even while the body sleeps, its nerve systems are active, continuously monitoring and adjusting the internal processes, and checking the outside world for danger. The heart never stops, but beats slower while at rest.