What Happens When you Sleep?



When you go to sleep, your brain doesn’t just turn off like a light and flick back on when you wake up. Sleep is complex, and takes the form of many stages. Each stage can be defined by the signals in your brain measured by an electroencephalogram (EEG) and other muscle and eye movements. Let’s take a look at each of the stages, and see why they are important. A sleep cycle is broken down into two halves; REM (Rapid Eye Movement) Sleep, and Non-REM sleep. Non-REM is then broken down further into four stages. Let’s start with the stages of Non-REM Sleep:

  • Stage 1 Sleep - The lightest form of sleep in the cycle. The measured brain waves are slightly slower than if you were awake. This is the easiest stage to be awakened from and it is common for people to experience a falling sensation via muscle contractions.

  • Stage 2 Sleep - At this point your brain waves continue to slow down. Physical signs of reaching this stage include a lowering of body temperature and lower hear rate.

  • Stages 3&4 Sleep - Considered the stages of deep sleep. Brainwaves at this stage are extremely slow with breaks of smaller faster waves. In this stage people can experience sleep talking, bed wetting, and sleep walking. These abnormalities occur when the brain is making the transition between Non-REM and REM sleep. Finally, being awoken from this state causes grogginess and the feeling of disorientation.

The last stage is REM sleep:

  • Stage 5 or REM Sleep- Your eyes remained closed, but shift rapidly back and forth. It is widely believed that this movement is related to dreaming and the brain activity that occurs during this stage. Measuring the brain activity reveals that your brainwaves are almost the same as if you were awake. Lastly, the muscles throughout your body (with the exception of the repertory system) are paralyzed.

A sleep cycle is determined by going through Non-REM to REM, and usually this cycle takes 1.5 to 2 hours. Interestingly, you don’t need to go through all four stages of sleep to reach REM. In addition, you can also repeat stages of Non-REM sleep before making the change from Non-REM to REM sleep. On average, a person will complete four to five sleep cycles through the night.


Sleep is vital to one’s health. Be sure to give yourself enough time to allow your brain to go through several sleep cycles so you get meaningful sleep!

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