We often think of sleep as the moment we close our eyes, shut off our minds, and drift off into dreamland. But did you know that sleep is much more than that?
As you probably already know, sleep is essential to our lives and well-being because it helps recharge, revitalize and refresh us so that our brains and every part of our being can function as they should. It is also one of the best ways to relieve stress, improve mood and reduce the risk of health problems.
How Many Stages of Sleep Are There?
The human body experiences two main stages of sleep. They include:
- The Non-Rapid Eye Movement Sleep Stage
- The Rapid Eye Movement Sleep Stage
During each night’s sleep, the body goes through an average of four to six cycles, each lasting about 90-120 minutes. Each sleep cycle can be divided into four phases:
- one rapid eye movement (REM) stage and
- three non-rapid eye movement (non-REM) stages.
Interestingly, different activities take place in each of these phases. Let’s take a closer look at each of them.
The Non-REM Sleep Stage
This sleep stage begins the cycle and can be divided into three phases: the N1, N2, and N3. You spend about 75% of your sleep time in the non-REM stage and most of it in the N2 stage.
1) The N1 Stage
The non-REM N1 stage is the starting point of sleep, where your muscles relax, and you transition from being awake to falling asleep. Usually, it lasts between one and five minutes. It is also called the “light sleep stage.”
The N1 stage is characterized by slow eye movements, reduced breathing, and heartbeats. If you are awakened at this phase, you will probably not realize that you have been sleeping. However, if you are not disturbed, you will quickly move on to the next sleep phase, the N2 stage.
2) The N2 Stage
As mentioned earlier, this non-REM N2 stage takes up most of your sleep time and occurs just before deep sleep. It lasts about 25 minutes in the first sleep cycle and increases in subsequent ones.
Typically, during this phase, no eye movement exists, your body temperature drops, and breathing, heartbeat, and brain activity slow down.
3) The N3 Stage
The N3 stage is the final non-REM phase which is characterized by no eye movement, a relaxed body, deep sleep, slower heart rate, breathing, and brain waves. It is also called slow-wave sleep (SWS).
Waking up from the N3 stage is a struggle. Those awakened during this phase usually experience 30 to 60 minutes of sleep inertia (a state of mental fogginess, low alertness, and high sleepiness).
Usually, it is difficult to wake some people from this phase, even in the presence of loud noise. Also, it is no surprise that acts like sleepwalking, nighttime anxiety, and bedwetting occur during this time as well.
This stage is also when the body performs various health-promoting activities such as tissue repair, bone and muscle building, and strengthening the immune system.
The REM Sleep Stage
This phase usually begins 60 to 90 minutes after falling asleep and lasts for about 10 minutes in the first cycle, increasing in duration in each sleep cycle and lasting up to 60 minutes in the last cycle.
The REM sleep stage is characterized by rapid eye movements, irregular breathing, increased brain activity, and lucid dreaming.
The REM stage consists of two phases: the phasic and tonic phases. Phasic REM sleep includes spurts of rapid eye movement, while tonic REM sleep does not.
When sleeping at night, you experience all these sleep stages several times every 90 minutes or so. And as the night progresses, there is a shift in sleep stages, with the first half of the night seeing an increase in the non-REM phase. However, the second half of the night sees an increase in REM sleep.
In Which Sleep Stage Does Snoring Occur?
Snoring is the loud breathing sound that occurs during sleep when the airflow through the mouth and nose is blocked.
Remember that the N2 phase of non-REM precedes deep sleep and features increased muscle relaxation and slower brain activity? In this phase, the throat muscles are so relaxed that the tongue falls into the back of the throat, blocking the airway and causing snoring.
Even though the N2 phase is essential and takes up most of your sleep time, deep sleep (N3) is the phase in which the body performs various repair and recovery processes. This makes it an equally essential part of the sleep cycle.
Unfortunately, snorers rarely spend enough time in the N3 phase because when their airway is blocked, the body will not get enough oxygen to move from the N2 phase to the N3 phase. And not spending enough time in the N3 stage means a person will often wake up tired, no matter how long they slept.
The importance of quality sleep to our lives and health cannot be overemphasized. And now that we have established how many sleep stages there are, it is important for us to actively tackle anything that disturbs us from going through every stage of sleep as required, as that goes a long way to determine how we will feel when we wake up.