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Health and Wellbeing

What Happens When You Sleep?

Dr Nerina Ramlakhan

Dr Nerina Ramlakhan

24th August, 2023

woman sleeping in bed with white sheets and wearing a blue shirt

Did you know that nature has designed us to spend roughly a third of our lives sleeping? Amazing processes take place when you sleep that enable you to wake up feeling restored on every level - physically, mentally and emotionally. Here’s what you need to know about what happens when you sleep.

Many important biological processes happen during sleep:

• The brain stores new information and gets rid of toxic waste.

• Nerve cells communicate and reorganize, which supports healthy brain function.

• The body repairs cells, restores energy, and releases molecules like hormones and proteins.

These processes are critical for our overall health. Without them, our bodies can’t function correctly. If you are not sleeping well night after night, it can take its toll on your energy levels, mood, concentration levels and physical health. It’s important to understand what happens when you sleep, so you can manage your lifestyle choices.

The 4 Stages of Sleep

Understanding what happens when you sleep is not only fascinating, but it can also help you to better manage your lifestyle habits and sleep hygiene so that you get the restorative sleep that you deserve.

When we sleep at night, we journey through four or five sleep cycles and each cycle is divided into 4 key stages. This is called your ‘sleep architecture’. Brain wave activity changes as you go through the various cycles of sleep. Here are 4 key stages to understand what happens when you sleep:

Stage 1: Non-REM (Rapid Eye Movement) Sleep

A short phase of light sleep, dozing off, transitioning into being asleep. Brain wave activity in this phase shows a predominance of high frequency, low amplitude alpha waves.

Stage 2: Non-REM Sleep

Now you are settling into sleep, your body and mind is relaxing into sleep and slower theta wave brain activity is more predominant.

These are the shallowest phases of our sleep during which we are most easily woken.

Stage 3: Deep Sleep (also known as slow wave sleep)

Your body is dropping down even deeper into sleep, brain wave activity slows down with a predominance of delta waves and you are in recovery and restoration mode. It is hardest for you to be woken during this stage.

Stage 4: REM Sleep

During periods of REM sleep, brain wave activity is similar to when you’re awake with a predominance of beta wave activity. This is when we have our most intense dreams. Breathing and heart rate increase during REM sleep but most of our muscles are paralysed, which keeps us from acting out those vivid dreams.

Each sleep cycle takes between 70 and 120 minutes. In the first sleep cycles of the night, more time is spent in non-REM sleep. The majority of REM sleep happens during the second half of the night. You might find that you remember your dreams when you wake in the morning and that’s because you probably had them in the REM stages of your sleep just before you woke up.

alarm clock in front of the night sky

How much of each type of sleep do you need?

It’s not just about getting 7 or 8 hours of sleep; you need both the right amount and type of sleep in order to function at your best. For the average adult who is getting around 7 hours of sleep per night, it is estimated that we spend around 20% in deep sleep. And we need around 2 hours of REM sleep per night.

The recommended amount of sleep depends on your age and varies from person to person but here are some rough guidelines:

• Birth to 3 months: 14 to 17 hours

• 4 to 12 months: 12 to 16 hours per 24 hours, including naps

• 1 to 2 years: 11 to 14 hours per 24 hours, including naps

• 3 to 5 years: 10 to 13 hours per 24 hours, including naps

• 6 to 12 years: 9 to 12 hours

• 13 to 18 years: 8 to 10 hours

• 18 to 60 years: 7 or more hours

• 61 to 64 years: 7 to 9 hours

• 65 years and older: 7 to 8 hours

It appears that deep sleep is important for restoration and recovery and during REM sleep is vital for dreaming, processing of emotions and memory consolidation. When you sleep you produce hormones that restore the body and these include:

• Melatonin – the important sleep hormone that helps you to sleep

• Growth hormone – supports bone growth and repair and muscle development

• Leptin and ghrelin – help control appetite

What happens when you have problems sleeping?

If you have sleeping problems, you may not get the full restorative benefits that come from what normally happens during sleep. The specific effects depend on the type of sleeping problem and its cause.

People with insomnia have a hard time falling asleep or staying asleep for as long as they want to, which means that they get insufficient total sleep. As a result, they may not progress through enough sleep cycles to get proper rest, leading to daytime sleepiness as well as negative effects on mood and thinking.

tired man with hands over his eyes wearing glasses

Sleep deprivation, which often occurs with insomnia, can throw off the balance of your sleep architecture. For example, after going without enough sleep, people often experience a REM sleep rebound in which they end up spending a disproportionate amount of time in REM sleep. This can cause too much brain activity, which in turn can leave you feeling irritable and may worsen mental health issues like anxiety and depression.

Sleep disorders such as restless leg syndrome or sleep apnoea can cause frequent awakenings that interrupt the normal sleep cycle impacting restorative sleep. Circadian rhythm sleep disorders can lead to insufficient sleep or abnormal sleep architecture – a typical example is going to bed very late and sleeping late into the next day. Oversleeping or hypersomnia can also affect the architecture of your sleep so people who oversleep tend to be excessively sleepy during the day and find it hard to stay awake when they need to.

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