otty sleep,

What happens when we sleep?

Amazing but true: we can live for longer without food than we can without sleep. But, while we have a better grasp of diet, the mind has always been something of a mystery.

Thankfully, it might not remain a mystery for long. Science is slowly starting to unpick the enigma of our dreaming hours with the advent of better technology, and what we’re only just beginning to understand about sleep is pretty fascinating already.

We spend an astounding 1/3 of our lives asleep so it stands to reason it must be pretty important. And as you’re about to find out, it’s doing more for your health than you might realise…


How do we fall asleep?

Historically, sleep was thought of as a time when our bodies went into a dormant state or simply shut off like a lightbulb. Now we know this isn’t the case; there’s actually a lot going on when we nod off.

Our brain remains active to varying degrees as we sleep. It’s just that its focus shifts from our waking processes, like eating, walking and talking, to the essential functions that run behind the scenes.

The Sleep Cycle

So, how do we actually get to sleep? It happens in four distinct stages, which are split into two different patterns of sleep: non-rapid eye movement (NREM) and rapid eye movement (REM). Both of these sleep types serve a different purpose, and our bodies will cycle through them multiple times a night to make sure we get the rest we need.

Sleep Stage

Sleep Type

Length of Time

Bodily Processes

Stage 1


1-5 mins

·       Body relaxes in preparation for sleep

·       Heartbeat, eye movement and breathing slows

Stage 2


10-60 mins

·       Body temperature drops

·       Decreased response to external stimuli

·       Sleep spindles occur

Stage 3


20-40 mins

·       Deepest stage of sleep

·       Muscles relax, brainwaves slow

·       Heartbeat and breathing slow to lowest levels

Stage 4


10-60 mins

·       Brain reaches levels of activity similar to when awake

·       Eyes move rapidly behind eyelids

·       Dreams occur

·       Body is temporarily paralyzed


Sleep Stage 1 – NREM

The first stage of NREM sleep is short and sweet. This is the point where we’re preparing our bodies to transition from being awake to being asleep.

Your breathing, heartrate and eye movement will begin to slow as you ease yourself into a restful state, and your muscles may occasionally twitch as they start to relax. You can be easily woken up at this stage. Or – as is quite common – you could even startle yourself awake, not realising you were drifting off in the first place.

Sleep Stage 2 – NREM

We spend an estimated 50% of our night’s sleep in this phase. At this point, your body temperature drops and you will become a little harder to wake up.

Stage 2 is an interesting phase because during this part of NREM sleep, we begin to sort through the memories and experiences imprinted onto our minds during the day. This happens through a pattern of brainwave activity called ‘sleep spindles’. Though sleep spindles are still being researched, it’s theorised that they are instrumental in processing and committing information to memory.

Sleep Stage 3 – NREM

Stage 3 is the deep sleep phase and the one that helps us to feel alert and refreshed the next day. It’s much harder to wake people up at this stage because your body is at its most relaxed. During Stage 3, brain activity slows to its lowest point and begins to produce something called delta waves, which is why this phase is often referred to as ‘delta sleep’ or ‘slow wave sleep’.

At this stage in the cycle your body undertakes important repairs. It also further consolidates information and memories that may be useful. Evidence indicates that delta sleep may also contribute towards the development of creative thinking skills.

Sleep Stage 4 – REM

REM sleep is predominantly the stage where we dream, or certainly when our dreams take on their most surreal, bizarre qualities.

Here, our brain activity is closest to its waking state. Rapid eye movement can be seen beneath the eyelids, with breathing and heartrate also increasing closer to waking levels. Since we wouldn’t want to accidentally act out our dreams (or deal with the chaotic aftermath), the body enters a state of paralysis during REM sleep, which can be very disorientating if you wake up during this stage.

It’s thought that at this point REM specifically assists with preserving and consolidating emotional memories. We’ll touch on this more below.

What does sleep do for us?

We’ve covered how we sleep, so now let’s take a closer look at the why. From what we know so far through scientific study, sleep covers a range of functions that are essential to our overall health. Its effects are far reaching and play a huge role in everything from heart health to mental wellbeing. In fact, it’s hard to think of a physical process that doesn’t benefit from a good night’s sleep.

Repairing and restoring the body

Time may be the greatest healer of all but sleep’s pretty good too. During Stage 2 NREM sleep, the pituitary gland releases growth hormones to tell our bodies to repair any damaged muscle or tissue. This is also the time when our immune systems are boosted to keep us healthy and provide maximum protection against viruses and bacteria.

Another essential repair function that happens during deep sleep is the removal of toxins from the neurons in the brain and nervous system. By keeping our synaptic pathways in tip-top condition, we can think more clearly the following day and react better to any challenges that come our way.

Stress reduction through sleep also goes a long way to improving our health. When we sleep, our blood pressure drops to ease the pressure on our circulation, and we also use this time to regulate our blood sugar levels. Lack of sleep, on the other hand, can cause undue pressure on the heart because it makes our bodies release the stress hormone cortisol, which makes our circulatory system work harder.

Sorting and organising memory

Human beings have managed to become the successful species they are in no small part to creative thinking. When we sleep, we spend a substantial part of it sorting through all of the information and memories gathered during the day, deciding what we want to keep and where we should store it in our minds.

In the case of NREM sleep, we sift through our memories, reorganising info to see if new patterns emerge. It really does help to sleep on a problem if you can’t figure it out. Your brain can make new connections in sleep that you might never put together during the waking hours. REM sleep also promotes creative thinking as you snooze. By creating a more abstract landscape, the dreamworld of REM sleep can help us to formulate more unexpected connections between information. It’s the ‘thinking outside the box’ exercise to your real world problems.

To get a bit techy here for a second, if your brain was a computer, sleep would be like defragging your hard drive. When you sleep, data is efficiently tidied away so that your brain runs more smoothly on a long-term basis. The brain’s ability to adapt, reorganise and create new connections to information is called neuroplasticity or brain plasticity, and it’s what makes humans great learners.  

Sleep as a therapeutic process

One interesting theory for REM sleep is that it could function as an important way of supporting our mental health.

Throughout REM sleep, the part of our brain that controls emotional memory becomes more active, and by paralyzing our muscles during this stage, it gives us the ability to explore any upsetting experiences (without accidentally injuring ourselves!) and potentially learn from them.

According to neuroscience professor, Matthew Walker, REM sleep is the only time when our bodies shut off a stress hormone called noradrenaline, which triggers a flight or fight response. This essentially gives us the scope to replay the more traumatic elements of our lives and view them from a comparatively safe vantage point. By removing our stress response, we are in a way distanced from the painful flashpoint of the memory and this could help us to lessen its burden over time.

Dreaming can often conjure strange and frightening imagery but REM sleep might be providing us with a core coping mechanism that makes us stronger in day-to-day life!  


Any sophisticated machine will need regular maintenance and this is no less true for the human body. Sleep acts as our nightly tune-up so we’re ready to face the day and give it our all. And while we still don’t know the whole scoop behind sleep, there’s certainly enough to underscore how crucial it is to our mental and physical health.

Sleep isn’t something to skimp on – there’s a good reason mother nature built us for a solid 8 hours of rest. Make your health a priority and give yourself the opportunity for full, unbroken rest every night. And if opportunity isn’t holding you back from better sleep, it’s well worth taking a look at your bedroom setup to see if you could make yourself more comfortable.


Research sources:

The Hidden Brain podcast

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