Have you ever wondered what happens in your sleep? Why are you easier to wake up at some points when you sleep than at other points? This answer lies within the sleep cycle. Your body goes through a few sleep cycles while you are sleeping to help you revitalize and make you feel rested.


What is the Sleep Cycle?

The sleep cycle lasts anywhere form 90-120 minutes

The sleep cycle is a set of different stages of sleep that you go through during sleep. The sleep cycle generally is completed within 90-120 minutes of sleep. There are five stages of sleep each varying in sleep depth.


What stages are there in the Sleep Cycle?

There are five stages of sleep that each have different significances. Each sleep stage takes anywhere from 5-15 minutes. You can go through multiple sleep cycles each night which can help make you feel well-rested. Each stage has a very, very unique name which include:

  • Stage 1
  • Stage 2
  • Stage 3
  • Stage 4
  • REM Sleep


Stage 1

Stage 1 sleep is the lightest sleep achieved. In this stage, breathing slows and the muscles start to relax. A person in this stage of sleep can experience sudden muscle contractions. If someone is awakened during this sleep stage, they will generally claim that they were never asleep since it is such a light sleep.


Stage 2

During stage 2, the brain waves slow as well as the heart rate. Stage 2 also presents a drop in body temperature and the stoppage of eye movement. This is the stage that prepares the person for deep sleep, stages 3 and 4.


Stage 3

Stage 3 is the first stage of deep sleep. During stage 3, the brain waves slow further and a person may experience various sleep disorders. These may include night terrors, bedwetting, sleepwalking and other various parasomnias. Parasomnias are sleep disorders that include atypical behaviors or movements.


Stage 4

The last non-REM sleep stage is stage 4. Stage 4 is very similar to stage 3 since it is another deep sleep stage. The main difference is that, in stage 4, the brain produces primarily delta waves rather than having delta waves mixed in with faster waves like in stage 3.


REM Sleep

The last sleep stage is REM Sleep. REM stands for Rapid Eye Movement which is what happens when someone reaches this sleep stage, their eyes move side-to-side very quickly. During this stage of sleep, you experience dreaming. Your body also does some pretty weird things like having irregular breathing, increasing your heart rate, making your brain activity become very similar to those of being awake, and paralyzing your muscles. It is hypothesized that humans have evolved to become paralyzed in their sleep which would keep them safer by preventing them from acting out their dreams. There is a certain disorder that does not paralyze you called REM Behavior Disorder. This disorder can cause you to act out your dreams when you are asleep which can cause you to hurt yourself and possibly others by punching, kicking, and yelling during your sleep.