There are 4 different stages of sleep. The length of these stages varies and the ‘role’ they have is also different. However, they are all important and completing a series of full sleep cycles, of all of the stages, is important for a good night’s sleep.
In this blog post, Dr Lindsay Browning explains the differences between stages of sleep and why they are important.
What are the stages of sleep and why do we need them?
Far from being a period of time where our brain “switches off”, there are actually a whole host of processes going on when we sleep. Our brain does this by moving through a series of different kinds of sleep called sleep stages. These stages happen in cycles of approximately 90-110 minutes across the night.
Each sleep cycle includes light sleep (N1 and N2), deep sleep (N3) and dreaming sleep (also called REM sleep) (R).
We don’t know exactly what the benefits of each stage are but we believe that deep sleep is where your body physically repairs and regenerates (like Dr Who!) and it is also where children produce hormones to help them grow.
However, it is not just deep sleep, but all of the stages that are important to support health and happiness.
Understanding each of the sleep stages
Light Sleep – N1
As you fall asleep you initially go in to the lightest stage of sleep (N1), during which you could be easily woken, for example, by someone lightly touching your arm or quietly whispering your name.
During N1 different parts of your brain start to fall asleep, but some times not quite all at the same time. N1 sleep can last between one and seven minutes at the start of the night (or when you fall off to sleep).
Light Sleep – N2
Next, you go in to N2 stage of sleep. This is still a light sleep but you are not so easy to wake now.
In the first sleep cycle, it can last between 10-25 minutes. You will actually spend most of your sleep time in this stage, overall.
Deep sleep – N3
In deep sleep, also known as slow wave sleep, you will be so deeply asleep that even a loud noise may not wake you. In the first sleep cycle, this stage lasts between 20-40 minutes. However, as we age we tend to get less and less deep sleep overall.
Children have extremely deep sleep, much deeper than adults, and can be very hard to wake, especially in the first sleep cycle.
Dreaming (REM) Sleep – R
After deep sleep comes dreaming sleep – stage R, also known as REM – which stands for rapid eye movement. It so named because your eyes will rapidly move beneath your closed lids. Unsurprisingly, this is the stage of sleep when you are dreaming. The first cycle of REM sleep tends to be shorter, but can last between 10-60 minutes through the night.
You are closest to consciousness when you’re dreaming sleep. In fact our brain activity looks very similar to when we are awake.
Sleep stages and how the sleep cycle repeats
With the end of dreaming sleep, the first full sleep cycle of the night ends. A brief arousal from sleep may occur before the next sleep cycle.
Each full sleep cycle averages around 90-110 minutes. Therefore, a full night’s sleep will contain 5-6 cycles. With each cycle we get less deep sleep and more dreaming sleep.
Waking up mid sleep cycle
If you wake at the end of a sleep cycle you are likely to feel good – this is why waking up ‘naturally’ usually feels nice and refreshing. However, if we are woken mid sleep cycle, by an alarm or other disturbance, especially if it is during a deeper sleep stage, then you will feel tried, groggy and disorientated. This is called sleep inertia.
The further from consciousness you were when you woke up the greater the inertia and more your body wants you to go back to sleep.
However, remember that how you feel the moment you wake up is more linked to the stage of sleep you were woken from, rather than the length or quality of your sleep overall.
This is why it is important to wait 10-15 minutes for your sleep inertia to pass and then assess how you are feeling and how well you slept.
Are all of sleep stages important?
Evolutionarily, sleep makes little sense since it requires you to be unconscious and vulnerable to attack by predators. Sleep must therefore be absolutely vital to our survival to outweigh the risk.
We know humans cannot survive without any sleep at all in the long term and regularly getting enough sleep (approximately 7-9 hours) has a great deal of benefits. Many studies have show that getting the right amount of sleep:
- Reduces anxiety and depression
- Lowers risk of
- heart disease
- stroke
- dementia
- certain hormonal cancers
- Type 2 diabetes
- Helps with a more robust immune system
Light sleep, it is believed, is important for forming long term memories. And dreaming sleep is where you process emptions and make sense of what happened during your awakes times.
Therefore, all stages are important and regularly completing a series of sleep cycles is important. You need them all to keep you healthy and happy.
Learn more about stages of sleep
Chapter 1 of my book Navigating Sleeplessness includes lots of information about the ‘science of sleep’, why it is important and what the stages involve mean. The book also includes information of the amount of sleep you need, understanding what is ‘bad sleep’ and also advises on changing sleep habits and how to help you get better quality sleep overall.
If you don’t own a copy, you can buy it here today: