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Sleep is our safe harbor to which we arrive at, no matter how complicated our life is. It’s then that our body repairs itself, and our mind sorts things out.
As with all good things in life, sleep is very well organized into different stages, each with its own mission. Today, we will look at what are the 5 stages of sleep and why they are so important.
What are the 5 stages of sleep?
Many of us don’t think about what happens while we sleep, unless we have a very vivid dream that wakes us up.
We are often under the impression that we start dreaming the moment we fall asleep. But even if some form of dreaming does take place at the beginning of the sleep cycle, most of it happens during the last phase of sleep – REM (rapid eye movement) sleep.
During the night we sleep in cycles. A cycle can last between 90 and 120 minutes and at the end of the cycle we wake up for a brief period of time (as short as a few seconds), then we fall back asleep[i].
Most people completely forget the fact that they briefly woke up, and that is perfectly normal. But there are those who have difficulty falling back asleep, and that is one of the most common causes of insomnia.
A sleep cycle is divided into 5 stages. All the stages of sleep are important. Together they help us perform a series of complex tasks like:
- Healing;
- Regulate hormones;
- Retain and manage memories;
- Eliminate toxins;
- Regulate the emotional status;
- Correcting neuronal imbalances.
You can read more on the importance of sleep and how its deficiency can affect us on the long term here, in the article that we dedicated to this subject.
During sleep, our brain waves change along with the stages of sleep. Brainwaves are just a fancy way of saying electrical impulses.
Our brain uses electrical impulses to communicate and these have a different strength measured in Hertz. These are the waves that you would see on an EEG, and believe it or not, they define who we are[1].
While we are awake and alert, our main brain wave is Beta. This means that we are able to concentrate, receive and interpret information that we obtain through our main senses.
Now, let’s look at the 5 stages of sleep and what they are all about.
Stage 1 – Non REM sleep (NREM)
This is the sleep phase that happens when you doze off. Everyone is familiar with the feeling. It’s the one when you lose the train of thought and it feels like you are dreaming, even if you are not.
This is when jerky movements appear occasionally, and you probably can relate those to the feeling of falling.
This is the phase of sleep that is the easiest to lose. Eyes still move a bit and can even be slightly open, while you can still hear noises from the environment, even if they are a bit tuned down.
When you first enter this sleep stage, your brain waves change. The main brain waves that dominate this sleep stage are called Alpha waves. These illustrate a state of relaxation that we can also find in meditation.
The muscles start to relax and the pulse lowers along with our blood pressure. The duration of this stage of sleep depends on how fast you can relax and on the environment (if you will be disturbed, you will stay in this state for longer).
Stage 2 – Non REM sleep
During this stage of sleep the muscles relax further, the blood pressure lowers and all the metabolic functions slow down.
The body temperature plummets, and this is why it’s important to have a relatively cool room temperature when you go to sleep.
This is a light form of sleep, dominated by Theta brainwaves that are occasionally interrupted by spikes called sleep spindles. Theta waves translate into enhanced relaxation and some may recognize this sleep phase by the feeling of floating.
This sleep phase lasts for an average of 20 minutes.
Stage 3 – Non REM sleep
This is the last stage before deep sleep and it reflects in the tone of the muscles, which are even more relaxed and in the response to external stimuli.
Someone who is in stage 3 of sleep will rarely respond to external stimuli and the brain waves are a combination of Theta and Delta waves with very little spikes in brain activity.
It usually lasts for about 10 minutes and it prepares the body for what is to come, by progressively shifting the blood pressure, pulse and brain waves.
Stage 4 – Deep sleep (NREM)
The type of brain wave that dominates deep sleep is Delta and this is when some of the magic happens. During stage 4 the body will start working hard at repairing muscles, cells and at removing toxins from the brain.
Even DNA and bone is being repaired at this stage, and the immune system is alert and active.
The muscles are still able to move, even if they are very relaxed, but it is very difficult to wake up someone who is in deep sleep.
The duration of deep sleep is directly proportional with how tired the person is. For this reason, during the first cycles of sleep, one can spend up to 40 minutes in deep sleep. But early in the morning, after a good night’s sleep, only a few minutes will be spent in deep sleep.
Stage 5 – REM sleep
REM sleep might be much more important than we think. The fact that we dream might be responsible for how we react to stress during the next day, as it helps us regulate our emotions.
This is true even if the dreams are actually nightmares. It’s a coping mechanism that our brain uses to help deal with the events of the previous day and to lay out the foundation for a healthy emotional status in the day to come.
During REM sleep, the brain waves are similar to those of a person who is fully awake, and the rapid eye movements are caused by the intense brain activity.
However, the muscles have no tone, all motion being suspended to prevent a person from acting out their dreams.
The duration of REM sleep is inversely proportional to the duration of deep sleep. So you will have shorter REM sleep periods at the beginning of the night, and longer ones towards the morning.
Another interesting fact is that newborns have a very long REM sleep (up to 8 hours/day), while elderly people have a very short one. The reason behind this is yet to be discovered[ii].
No matter how much of your dreams you remember, one thing is clear. Sleep is extremely important for our health, and we must do all we can to make sure that we get enough high-quality sleep.
[1] https://my.clevelandclinic.org/health/articles/12148-sleep-basics
[i] https://www.brainfacts.org/archives/2012/the-different-kinds-of-sleep
[ii] https://www.ncbi.nlm.nih.gov/books/NBK10996/
