Learn About the Stages of Sleep

The typical sleep cycle lasts 90 minutes and has four stages of sleep.

We are said to spend about a third of our lives sleeping, but how many of us actually understand what happens during sleep? We know about sleep deprivation and often do our best to improve our sleep, but may not necessarily think about the process of sleep in itself.

This article offers a basic overview of the stages of sleep. 

The sleep cycle

The sleep cycle has four stages of sleep: stages one through three, and then Rapid Eye Movement (REM) sleep.

Each cycle lasts approximately ninety minutes to pass through. On average, people go through about five of these cycles nightly.

Stage One

Stage one sleep is characterized by a very light sleep from which you are easily woken. It lasts about five to ten minutes. Your eyes are closed but moving, and you may feel awake. 

Stage Two

In stage two, your eyes stop moving, your heart rate and brain waves slow down and your temperature begins to drop. Your body is preparing itself for the deeper levels of sleep it is about to fall into. 

Power naps are known for lasting about twenty minutes. They are kept to this short length of time so that one does not fall into the deeper stage three of sleep, which is harder to wake up from. When you wake up from a nap from stage two sleep, you will be more alert and less groggy than if you wait until you reach the deeper levels of sleep.

Stage three

During stage three, the body falls into a deep sleep.

Very slow brain waves known as delta waves take place. Smaller and faster brain waves may be interspersed throughout, but eventually, this level of deep sleep may consist almost exclusively of the very slow delta brain waves.

There was also once a stage four of sleep, which was the deeper level of stage three with primarily delta brain waves, but in 2008, stages three and four were combined by the American Academy of Sleep Medicine.


It can be hard to wake someone up from this stage of sleep. During this time, the body is regenerating tissues and rebuilding muscles. No eye movement occurs in stage three. This is also the stage of sleep in which children may wet their beds, night terrors occur, and sleep walking happens.

REM sleep

The final stage of sleep is REM sleep, known for the "rapid eye movement" that occurs during this time. REM sleep is also characterized by rapid, irregular and shallow breathing, more active brain waves, a faster heart rate, and dreams. Typically when woken up from REM sleep, one can remember his or her dreams. Interestingly, the arms and legs are temporarily paralyzed during this stage of sleep.

In the first cycle of sleep, the REM phase lasts about ten minutes, but gets longer with each subsequent cycle. The final phase of REM sleep can last as long as an hour. Babies spend about half of their sleep time in REM sleep, but this reduces over time, with about twenty percent of adult sleep being REM sleep.

Next time your alarm goes off, see if you can identify which stage of sleep you were woken from.



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