What happens to your body when you sleep?

By Mosh

09 September 2021

minute read

What happens to your body when you sleep?

Each night, as we lay down in bed, our bodies undergo a remarkable change: we leave waking consciousness, and for hours, enter a world of dreams and sleep cycles.

This complex state and why we need it has mystified scientists for thousands of years. And while we still have a lot to learn about why we sleep and dream, modern research is helping us to better understand what sleep does for the body and mind.

Our restful slumber serves to clear waste from the brain, support learning and memory and boost the body’s immunity. It even plays a vital role in regulating mood, appetite and libido. It’s no wonder we spend one third of our lives horizontal!

Each night, as we lay down in bed, our bodies undergo a remarkable change: we leave waking consciousness, and for hours, enter a world of dreams and sleep cycles. 

This complex state and why we need it has mystified scientists for thousands of years. And while we still have a lot to learn about why we sleep and dream, modern research is helping us to better understand what sleep does for the body and mind.

Our restful slumber serves to clear waste from the brain, support learning and memory and boost the body’s immunity. It even plays a vital role in regulating mood, appetite and libido. It’s no wonder we spend one third of our lives horizontal!

How the body changes during sleep

Before the modern era of sleep research in the 1920s, physicians believed that our brains were inactive during sleep. But now, thanks to our ability to measure brain, muscle and eye activity as we rest, we know that the opposite is true – the brain and body are in fact quite active at this time.

Within a minute of falling asleep, body temperature drops, brain activity slows, and heart rate and respiration decrease too. But this altered state isn’t static throughout the night. Sleep is a dynamic process, and over the course of one night, we progress through multiple sleep cycles, each of which lasts on average 90 minutes and is made up of different sleep stages. 
 

The two main sleep stages

The brain change patterns that happen during sleep have been classified into two main types — rapid-eye-movement (REM) sleep and non-rapid-eye-movement (NREM) sleep. NREM is further broken down into three distinct stages: N1, N2, and N3. These stages are divided based on the size of the brain waves: 

  • N1 is the stage between being awake and falling asleep. It typically lasts less than 10 minutes. In terms of brain wave activity, this stage is associated with both alpha and theta waves. The sleepier a person gets, the further he/she will move from alpha to the even lower frequency theta waves.

  • N2 represents slightly deeper sleep. It lasts 30-60 minutes. Theta waves still dominate the activity of the brain at this stage, but they are interrupted by brief bursts of activity known as sleep spindles – a rapid burst of higher frequency brain waves that may be important for learning and memory.

  • N3 is the deepest stage of sleep and lasts 20-40 minutes. It is characterised by much slower frequency, high amplitude signals known as delta waves. This stage is the most difficult to wake someone from. It’s the stage when the body repairs and regrows its tissues, builds bone and muscle, and strengthens the immune system.

REM sleep is the final sleep stage and the one associated with dreaming. At this time, the eyes move rapidly behind closed lids, and brain waves are similar to those during wakefulness. However, the body becomes temporarily paralysed – a protective mechanism that is thought to prevent us from "acting out" our dreams. 

REM sleep usually starts 90 minutes after falling asleep and the first cycle lasts about 10 minutes. As sleep progresses, REMs cycles get longer, with the final cycle lasting up to an hour.

Why are sleep cycles important?

Cycling through all the stages of sleep is important because it allows the body to recuperate and develop. On a typical night, most people will cycle through the different sleep stages four or five times. However, those with sleep difficulties may struggle to achieve this. As a result, they may experience some of the profound consequences of lack of sleep, including impaired thinking and reaction times, poorer emotional control and a higher chance of developing chronic health conditions.

Read more about why lack of sleep is bad for your health.
 

What can disrupt your sleep cycle?

While there is a typical pattern for sleep cycles, these can vary for individuals based on a number of factors:

  • Age – Our sleep patterns change as we age, with older adults tending to wake up early in the morning and fall asleep earlier in the evening. There is also less time spent in the deeper stages of sleep, which can lead to more disrupted – and therefore poorer quality – sleep.  

  • Chronic illnesses – The pain and fatigue of chronic illnesses can have a large impact on a person’s sleep. Conditions may include arthritis, Alzheimer’s disease, depression, anxiety and many more. Even drugs used to treat these conditions can interfere with sleep.

  • Irregular sleep patterns – If you get irregular or insufficient sleep over a few days or more, sleep cycles can be disrupted. This is common for shift workers, people with jet lag, and even those who regularly work late nights.

  • Alcohol – Drinking alcohol before bed can suppress REM sleep during the first two cycles. While alcohol is a sedative and can often bring about deep sleep quickly, as the night progresses, it can create an imbalance between slow-wave sleep and REM sleep, resulting in poorer sleep quality and duration.

  • Sleep disorders – Insomnia, sleep apnoea, restless leg syndrome and other conditions that cause multiple awakenings during sleep may interrupt a healthy sleep cycle.

How to optimise your sleep

It's clear that sleep is an important contributor to the proper functioning of nearly all of the systems of the body, so how can you ensure you get quality shut-eye?

Establishing good sleep hygiene is the best place to start. Read more on this in ‘How to treat sleep difficulties’.

However, if lifestyle changes aren’t enough for you, arrange a chat with a Mosh doctor online to discuss your other options.

Let’s get started!