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What happens when we sleep: 4 stages of quality rest

We’re all aiming for that seven to nine hours of nightly slumber to be well-rested for the day ahead. But how much do you know about what actually goes on when you sleep and its role in keeping you healthy?

It’s as much about quality as quantity. Our new Vhi Health Insights report into the impact of poor sleep on corporate employees found that there is a degree of confusion surrounding what constitutes valuable rest. So how can we distinguish poor sleep from quality sleep?

To do so, we must understand the four stages of sleep our body requires on a nightly basis…

Stage 1: The period when we first fall asleep, which occurs once in a night of uninterrupted sleep. Stage 1 typically lasts for 13 to 17 minutes as our heartbeat and breathing becomes regular, muscles relax and our body temperature falls. External stimuli start to fade away, though even slight noises or disturbances can stir us – you might not even realise you’d been asleep. 

If you’ve ever felt the sensation of falling in bed, that occurs during stage 1. Roughly 10% of our night will be spent either awake or in stage 1.

Stage 2: The second part of the light sleep phase makes up about half of our total sleep time. Sleep becomes deeper, muscles become fully relaxed and our eyes stop moving. The brain’s activity starts operating at a lower frequency. We will return to stage 2 several times as it is an important transition period.

Deep sleep: The most restful part of sleep. Your brain is producing slow-moving delta waves, with blood redirected from your head to your muscles. Your heart rate and breathing is at its lowest level and working rhythmically. Movement is very limited and it can be very difficult to wake someone from this state. 

It is now that the body repairs itself, building bone and muscle and strengthening your immune system. We should spend about 20% of our sleep time in this state, though that percentage drops as we age.

REM sleep: Named after the rapid eye movement it brings on, this is when you dream. The transition from deep sleep to REM sleep should occur 80 to 100 minutes after falling asleep and the abrupt switch may be signalled by a change in sleeping position.

Once you are in REM sleep, your heart rate and breathing will quicken. Your brain’s electrical activity can be as high as when you are awake. Your body will be in state of near-paralysis – this helps ensure you don’t act out your dreams.

REM sleep should account for roughly 20% of your time asleep. This percentage is much higher for very young children, likely due to their need to process lots of new information.

The sequences of events

It generally takes between 90 and 110 minutes to complete one sleep cycle. Your night will begin with the light sleep phase, before you move into your first period of deep sleep and then a short REM phase.

Later sleep cycles will find you spending less time in deep sleep as your REM phases get longer. The vast majority of deep sleep occurs in the first four hours. Your final phase of REM sleep can last for up to an hour or more before you wake in the morning.

Why each stage is vital

If you are operating on reduced sleep, it is the light sleep stage that will take the hit. This is fine short-term, but light sleep enables you to healthily access deep sleep. Both light sleep and deep sleep are needed to regenerate your internal systems.

Along with deep sleep, REM sleep is essential for processing and organising your memories and thoughts. It stimulates the parts of the brain used for learning. So, when you want to remember, say, the contents of a sleep article you’ve just read, that’s where REM comes into play.

For more articles on sleep, click here.