We all know how sleep looks -- when we see someone sleeping, we recognize the following characteristics:

* If possible, the person will lie down to go to sleep.

* The person's eyes are closed.

* The person doesn't hear anything unless it is a loud noise.

* The person breathes in a slow, rhythmic pattern.

* The person's muscles are completely relaxed. If sitting up, the person may fall out of his or her chair as sleep deepens.

* During sleep, the person occasionally rolls over or rearranges his or her body. This happens approximately once or twice an hour. This may be the body's way of making sure that no part of the body or skin has its circulation cut off for too long a period of time.