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Sleep explained

Written by Healthwords's team of doctors and pharmacists based in UK | Updated: 26.01.2023 | 2 min read

What is sleep? And why is it so important? Well, around a third of your life is spent sleeping and it is as necessary for survival as water and food. We'll explain here about the cycles of sleep and why we need them.

So what is sleep?

When you sleep your body goes through 5 different sleep stages in around 90 minute cycles. It is around 5-6 of these cycles that make up a good night’s sleep and allow you to feel refreshed. This is where the recommended 7-9 hours sleep per night comes from. The different stages of sleep provide different functions in order to help your mind and body recover and repair. If you wake up in the middle of a 90 minute cycle you can feel quite groggy compared to waking up at the end of a cycle.

Sleep stages one to three

Sleep stages one to three make up what’s known as light sleep. Its function is to help prepare your body for deep sleep. To do this, your heart rate and body temperature start to decrease. In stage one, you can rapidly return to being fully awake and it is in this stage some people get the sense of falling or jerking. This gets less likely in stages two and three.

Sleep stages four and five

Stage four of the sleep cycle is called deep sleep and this is where your body recovers and repairs. Stage five is called rapid eye movement sleep (also known as REM sleep). This is the stage when you dream and it is mind repairing which means it can help with mood, learning, and concentration. The dreaming that occurs in REM sleep can also help you process emotions.

How your body moves between the stages

In the first few 90 minute cycles of continuous sleep, you move through the 5 different stages of sleep but you have a longer time in deep sleep than you do in REM sleep. This then changes when in the latter half of a continuous sleep you begin having proportionally more time in REM sleep. Because deep sleep is body repairing, and REM sleep is mind repairing, the first 4-5 hours of continuous sleep help you physically repair, and the hours after that help your mind repair. If sleep is repeatedly cut short you may miss out on important time where your mind is able to repair and cope with all the complexities life asks of us; emotional strain, concentration, impulse control, decision making.

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