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What happens when I sleep?

Your body doesn't simply shut down as soon as you fall asleep. In fact, it's hard at work helping every mental and physical aspect of you function properly. No wonder the day after a bad night's sleep seems so terrible -- you didn't get to properly recharge.

From memory, to mood, to heart health, to your immune system and metabolism, there's pretty much nothing that sleep doesn't benefit.

The brain of an awake and relaxed person generates alpha waves, which give consistent oscillations at about 10 cycles per second. An awake and alert person generates beta waves, which are about two times as fast.

During sleep, two slower patterns - theta waves and delta waves - take over. The oscillations for theta waves are about 3.5 to 7 cycles per second. Delta waves oscillate less than 3.5 cycles per second. As a person starts to fall asleep and when sleep deepens, the brainwave patterns slow down. Slower brainwave patterns mean deeper sleep - a person deep in delta wave sleep is very hard to wake up.

At several points through the night, rapid eye movement (REM) sleep occurs. Most people have three to five intervals of REM sleep per night. Brainwaves during this period speed up to awake levels. Watch a person or a dog experience REM sleep. You will see the eyes flicker back and forth rapidly. In most dogs and some people, arms, legs and face muscles twitch during REM sleep. Periods of sleeping other than REM are called NREM (non-REM) sleep.

You dream during REM sleep. If you wake a person during REM sleep, that person can vividly recall dreams. During NREM sleep, however, generally the person will not be dreaming.

Everyone needs both REM and NREM sleep for a good night's sleep. A normal person will spend approximately 25 percent of the night in REM sleep. The rest is spent in NREM. A REM session - in other word's, a dream - lasts five to 30 minutes.

Scott M. Leibowitz, MD
Sleep Medicine

In the past, sleep was thought to be a state where we essentially hit the "pause" button until we wake up again and hit "play". Over the last 50+ years, we have come to understand sleep as a critical state where our body takes on a different physical state and our mind enters into different states of consciousness. With sleep onset, our physical processes, from cardiovascular function to brain function change, which allow for restoration and rejuvenation-- allowing us to wake up feeling better than we did when we went to sleep.

While we typically think of sleep as one state and wake as another, sleep is actually divided up into 2 different categories- Non-REM sleep and REM sleep. REM sleep is where we typically do most of our dreaming. Importantly, the physiology of brain and our body during REM sleep is as different from Non REM sleep as Wake is from Non REM sleep.

No one knows for sure why we sleep but it is clear that we must sleep and that through an optimal amount and quality of sleep, we function optimally in terms of our ability to think, process, problem solve, as well as perform athletically. It is also becoming increasingly clear that insufficient sleep and poor quality sleep associated with various sleep disorders leads to medical and psychiatric problems, obesity, and even increase likelihood of death.

Sleep is a physiological process that affects every organ system of the body. It is a state of unconsciousness that is different from coma and relaxation with the eyes closed. Sleep has well defined stages and is divided into two alternating categories: non-REM and REM sleep. An adult will enter sleep through the lightest stage of non-REM sleep (Stage 1) and progress through several non-REM stages (getting deeper from stage 2 to stage 4) until reaching REM sleep. These stages are defined by the waveforms that the brain produces (EEG) and gradual decrease of muscle tone to eventual muscle paralysis (during REM). Heart rate, respiration and even circulation slow during the various stages of sleep. Sleep appears to occur in cycles (of Non-REM and REM) at a predictable rate of between 80-120 minutes. The average person has 5-6 cycles.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.