Did you know that sleep does NOT mean the brain is resting? It's more appropriate to say that the brain never sleeps. In fact, the brain is extremely active during sleep. The one absolutely defining difference between wakefulness and sleep is that when we are awake, we are conscious of the real world. At the moment of sleep, our awareness of the outside world is completely shut down and we are conscious only of the inner world. Sleep also is characterized by little physical activity.
Another important feature of normal sleep is that it can end quickly. Unlike someone who has been knocked out, is anesthetized or in a coma, a sleeping person only appears unconscious and can be easily awakened and resume normal waking activity within a few minutes.
Okay, so why the heck do we need to sleep? Well, to be honest, no one really knows. Most scientists think that sleep does something important, something vital for life. Research has shown a lot of ways that sleep can help us, like consolidating memories, but it hasn't identified yet specifially what sleep does. Nevertheless, we all know when we need to sleep--we can feel this need. We also when sleep has done its work--we feel rested and that we have slept enough.
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