t may surprise you to learn that during the hours you seem to be "out cold," a lot is actually happening.

Normal sleepers have a relatively predictable "sleep architecture," the term used to describe an alternating pattern of REM (rapid-eye-movement) and non-REM sleep.

REM sleep is when you dream, and is characterized by a high level of mental and physical activity. In fact, your heart rate, blood pressure and breathing are similar to what you experience when you are awake.

Scientists define the best sleep as having the right mix of REM and non-REM sleep.

Getting enough sleep without interruptions from your environment or from internal factors such as your breathing is more likely to maintain your natural sleep architecture and result in restful and restorative sleep.