What is sleep?

What is sleep?

What is sleep?

It’s when neurotransmitters, the nerve-signalling chemicals in our bodies, stop producing serotonin and norepinephrine, which keeps our brain active and awake.

Instead, these neurons switch off. At the same time, a chemical known as adenosine, builds up in our blood, causing drowsiness.

There are four different stages of sleep:

  • Stage 1: Light sleep – the phase between being awake and falling asleep.
  • Stage 2: The onset of sleep – body temperature drops.

You may have experienced ‘hypnic jerks’ where you jump awake, or dream of falling off a curb or out of a plane…quite startling!

This is quite normal. It can sometimes happen when our body and mind are winding down at different rates.

If you find the frequency of hypnic jerks increasing beyond what is normal for you, working on the quality of your ‘you time’ before bed and making sure you have a consistent sleep pattern can help to reduce them.

  • Stage 3: Deepest and most restorative sleep takes place my favourite part (more on this below).

Note: It is known as the ‘healing phase’ because it’s when tissue growth and repair takes place, hormones are released and energy’s restored. It is the most difficult to rouse someone from this state. 

  • Stage 4 (REM): Takes place around 90 minutes after falling asleep and again every 90 minutes, getting longer later in the night.

Often REM is referred to as ‘dream’ sleep. It is true that some of the more graphic detailed dreams happen here, but we do actually dream in other areas of sleep too.

Often remembering our dreams is a sign of REM disruption. We all dream regardless of whether we remember or not.

REM is a very sensitive area of sleep, meaning it's quite easy for it to be disrupted - something that is more common as we get older.

What happens during deep sleep?

The middle stage of sleep (stage 3) is when we experience deep sleep, which is also known as slow-wave sleep or delta sleep.

When we deep sleep our:

  • Heartbeat, breathing and brainwaves slow down
  • Muscles relax

In turn, deep sleep can help: our brain process and store away memories, let our minds switch off, regulate our hormones, boost our immune system, keep our blood sugar down and make us feel more energised for the day ahead.

If you’re truly in a deep sleep, then you won’t wake up to loud noises. A bit like REM, deep sleep happens in regular phases. The first can last between 45 and 90 minutes and for longer as the night goes on.

We have a higher percentage of deep sleep in the first half of the night, and a higher percentage of REM sleep in the second half of the night.

That means sleeping after midnight is just as important as sleeping before midnight, contrary to the old wives tale!


Arguably, deep sleep is the most important part of our sleep. This is why we developed Deep Sleep + Full Restoration, the main portion of sleep this improves is the deep sleep. As a result of creating something that improves our deep sleep, all other sleep stages are effected positively.


Regardless to how well you sleep at the moment, we can all benefit from further improving our sleep health. The better we sleep, the healthier and happier we are as a result.

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