There are four stages of sleep—N1, N2, N3, and rapid eye movement (REM). And understanding each can help you get the best sleep possible.
The 4 Stages of Sleep—What Happens While You Sleep
What Are the Stages of Sleep?
The stages of sleep are divided into two categories—non-rapid eye movement (non-REM) and rapid eye movement (REM).
Non-REM is further divided into three stages—N1, N3, and N3.
N1 through N3 are the first stages of sleep until you move to the final step—REM sleep.
The deeper into the stages you go, the more difficult it is to wake you.
N1 | Non-REM Stage 1
Falling asleep stage.
N1 is when you begin to fall asleep.
It’s the shortest of the stages, lasting only five to 10 minutes. And if it goes uninterrupted, you can quickly move to N2. But if you are woken during the stage, you may not feel like you’ve slept.
What happens during N1?
- muscles relax
- eye movement activities slow down
- lower heart rate
- breathing slows down
- brain waves reduce to four to seven cycles each second
As you’re falling asleep, you may feel a limb jerk. It’s called a hypnic jerk or motion hypnic myoclonic. It’s perfectly normal and is no cause for concern.
N2 | Non-REM Stage 2
Believed to be important for memory consolidation and maintaining sleep.
This is the first phase of actual sleep and lasts between 10-25 minutes.
What happens during N2?
- muscles relax further
- eyes become still
- body temperature drops
- brain waves slow with occasional sleep spindles (quick burst of brain waves)
- K-complex (long, delta waves) may appear in EEG readings
K-complexes are delta waves that researchers think may help in memory consolidation and keeping you fast asleep. Noise—like someone calling your name— can activate these waves, which leads some scientists to believe that this might be a vigilance mechanism.
If you’re prone to teeth grinding (bruxism), this is the stage where it most likely occurs.
By the end of this stage, your body is prepared to go into a deep sleep and it will be much more difficult to wake you.
N3 | Non-REM Stage 3
At this stage, the body repairs itself, builds muscle and bone, and boosts the immune system. Evidence shows that it’s also important for brain power.
N3 is also called slow-wave sleep (SWS) or deep sleep. It’s the longest of the non-REM stages, lasting 20-40 minutes.
- blood pressure drops
- pulse slows to 20%-30% of waking rate
- very slow delta brain waves appear
- zero eye movement
- no muscle activity
If you tend to sleepwalk, wet the bed, or experience night terrors, this is the stage where it likely happens.
Be sure to prepare a good sleeping environment if you’re about to take a nap. Waking up in the middle of N3 will leave you groggier (sleep inertia) and more tired than before you closed your eyes.
Studies show that waking up in the middle of this stage may hurt your mental performance for 30 minutes up to an hour.
Older adults tend to spend less time at this stage, getting barely any deep sleep. On the other hand, young adults may spend 20%-25% of their sleep cycle in this stage.
REM sleep is when our brain is most active and plays a key role in learning and memory.
This is the final stage of sleep and concludes one full sleep cycle.
What happens during REM sleep?
- eyes move rapidly from side to side
- pulse rate picks up
- brain waves similar to wakefulness
- muscles are temporarily paralyzed
Sleep research shows that it’s during REM sleep that your brain organizes new information you learned. And at this stage, your brain works hard to regulate your mood and maintain good cognitive performance.
It’s also during this time that you dream, which may explain why your brain activity behaves as though you’re awake.
You spend more time in the REM stage as the night progresses. Your first episode of REM sleep might be as short as 10 minutes and the final episode could last as long as an hour.
Understanding the Sleep Cycle
There are four stages of sleep—N1, N2, N3, and rapid eye movement. And completing all four stages makes up one sleep cycle.
Ideally, we sleep through 5-6 cycles to get a full night’s rest.
The first cycle is typically the shortest one, lasting around 70-100 minutes. As the night progresses, how much time you spend in each stage may change. And your sleep cycles may average between 90-120 minutes.
What Influences the Stages of Sleep?
Multiple factors can affect the duration of your sleep cycle, like:
- current sleep pattern
- alcohol intake
- some sleep disorders
However, how long you stay in each stage can also vary per person. To make the most of your sleeping hours, make sure to create the perfect sleeping environment and follow proper sleeping hygiene.
If your mind feels foggy, or if you still feel tired in the morning, or you fall sick more than usual, look back to the quality of your sleep. Clean up your sleep habits and adopt new ones that might help you sleep better.
It might take some trial and error to see what works for you. But it is a long-term investment towards your health. And the returns will be ten-fold.
Each stage is essential to good sleep. Only when we’re able to smoothly move through each stage can we get truly restorative and refreshing sleep.
The Stages of Sleep—Keys to Good Health
The four stages of sleep include N1, N2, N3, and REM sleep.
In N1, we begin to fall asleep and our body goes into bedtime mode. It’s still easy to wake you, so be sure to keep the room quiet. Your brain starts consolidating and organizing your memory in N2. but sleep scientists think that a part of your brain might stay alert to immediately wake you if needed. And in N3, you go into a deep sleep and your body goes into full repair and rebuild mode as well as supports other bodily processes that keep you in top shape.
During REM sleep, in addition to conjuring up dreams, your brain works to improve your learning and memory.
Each stage of sleep is vital to deep and restful slumber, and a healthy brain. Poor sleep quality or failing to complete a sleep stage can lead to poor health or cause you to remember your notes for the next day’s important meeting.
Practice good sleep hygiene to get the best sleep possible. A warm bath before bed or investing in a new hybrid mattress can help move you through each stage of sleep and secure your health for tomorrow and decades from now.
Do you now have a better understanding of the different stages of sleep and why each one is important to restful slumber? Which facts were you surprised to learn? Which stages do you think you’re habitually missing out on? Share your thoughts with us in the comments section below! We’d love to hear from you.