The 4 Stages of Sleep
Non-REM & REM Sleep Cycles
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You will pass through 4-stages of sleep during the night, with a complete sleep cycle taking 90 to 110 minutes on average, with each stage lasting between 5 to 15 minutes.
Sleep is far more complex than you think, and while getting enough sleep is important, getting enough of the right kind of sleep is equally so. In order to do so, you need to educate yourself on the sleep cycles and what their purpose is.
What Are Sleep Cycles?
There are two types of sleep: NREM and REM. The latter is a stage on its own, where the former has three stages in the category.
You enter a new cycle every 90 minutes on average, but for some people, it may be closer to every 2 hours. This equals 4–5 full cycles throughout your slumber.
The various stages of NREM sleep transition you from light to deep, after which you enter REM sleep. Your first REM cycle lasts about 10 minutes, then you’re back to light NREM sleep to repeat the cycle.
Do Sleep Stages Matter?
Sleep stages absolutely matter and a healthy sleep cycle is an important element of your overall health.
Your brain and body need to recharge and heal themselves from any injuries, illnesses, and fatigue of the day. Failure to get enough sleep in each stage can lead to decreased mental cognition, undesirable emotions, and poor physical health.
There are also connections between sleep deprivation and weight gain and in women, acne.
Insomnia, sleep apnea, and other sleeping disorders may result in inadequate or insufficient sleep. The negative consequences are part of why these disorders are so serious, and why the sufferers tend to feel so poorly when their condition isn’t under control.
You cannot afford to skimp on any of the sleep stages. Alongside that, waking too early or struggling to sleep at all can cause shorter sleep cycles—which impacts the health of your overall sleep time.
The Stages of Sleep
We’ve got the basics covered—let’s get into the specifics of the sleep cycle’s four stages and how each impacts your health.
Stage 1 (N1)
This first stage of sleep is what you enter right after you drift off. It’s extremely light, so this is the stage where it’s most easy to wake you.
Your Eyes
Your eyes don’t move much during stage one of sleep. They move, rolling up and down gently, but not enough to be anything of note.
Your Body
As you enter stage one, your muscles relax and let your body heal itself from its antics throughout the day. You may feel some jerking or experience muscle spasms during this stage, but it’s not common.
Your Brain
During this stage your brain waves slow down, letting it get that much-needed rest. You won’t typically dream during this stage of sleep and if you do it will resemble that hallucinogenic state between awake and asleep.
Moving On From Stage One
Stage one of sleep only lasts a maximum of five minutes, so it’s not difficult to swiftly slide into stage two. It’s unlikely that you’ll spend much more time in this stage throughout the night.
Waking Up During Stage One
If you wake up during stage one sleep you’re likely to be very alert. If woken before entering stage two, you may feel as though you were never asleep.
If you happen to wake during a brief stage one stint later in the night, you may feel as though you were never asleep to begin with—despite the obvious passage of time. You won’t feel rested.
Stage 2 (N2)
After your brief time in stage one, you move onto stage two which is generally regarded as the first real light sleep stage.
Your Eyes
During this stage your eyes become still, matching your body.
Your Body
Your body grows stiller during this stage, your muscles relaxing further. You’re unlikely to spasm or move much during this part of your sleep. Alongside this, your body goes into a standby-like state. Your temperature lowers, along with your heart rate. Your breathing slows down to match. While this is still light sleep, you’re heading for a deeper stage.
Your Brain
Your brain starts working more once you’re out of stage one, into stage two. It’s not much—just short bursts that help you stay sleeping despite noises and sensations in your sleeping space.
Moving On From Stage Two
Stage two sleep gets longer throughout the night with the first stage lasting 10–25 minutes. This stage makes up around half of your total sleep time and is the predecessor to the all-important deep sleep.
Waking Up During Stage Two
As stage 2 is still light sleep, it’s best to be woken up during this time. Waking up during stage two sleep usually has people feeling well-rested and refreshed.
There are many apps and smartwatches that detect when you’re in light sleep and strive to wake you up so it’s easier for you to start your day.
Stage Three, (N3 or Deep Sleep)
Finally, we reach deep sleep, the most restorative part of the cycle. Experts agree that this stage of sleep is vital to help your creativity and ability to think insightfully flourish. They also believe it helps with memory.
Your Eyes
Your eyes are once again still during deep sleep—in fact, your body doesn’t move at all due to its advanced relaxed state.
Your Body
In stage three sleep, your body reaches its peak relaxation, slowest heart rate, and steadiest, calmest breathing. This is the part where your brain and body really get to rest—most of the time. On the other hand, if you suffer from sleepwalking, this is the stage where it occurs.
Your Brain
Your brain, despite resting, is relatively active during this stage of sleep. There are odd patterns of brain activity that are unidentifiable but present. The patterns are called delta waves.
These delta waves are slow but measurable and result in stage three or deep sleep being called delta sleep at times.
Alongside these waves, your dreams become more intense but it’s usually nothing vivid. When you have night terrors, they occur during deep sleep most of the time—although you’re most likely to forget them unless they wake you up.
Someone sharing your bed is likely to notice your sleep terror during this stage, as your body is not yet locked in place.
Moving On From Stage Three
You move on from this deep sleep quickly most of the time. You spend most of the first part of the night in deep sleep, for 20–40 minutes at a time. However, you spend less time in deep sleep as the night goes on as your time spent in REM increases.
Although, if you’re sleep deprived you’re likely to spend more time in deep sleep. It restores your exhausted mind and body, including your immune system. That’s why people suffering from illness are encouraged to rest a lot—your immune system repairs better in sleep than in waking life.
Waking Up During Stage Three
It’s highly unlikely that you’ll wake up during deep sleep. Deep sleep is usually the culprit for you sleeping through your alarm. It’s also the part of sleep that leads to a groggy and unsatisfied wake-up.
Stage 4 (REM)
Your Eyes
Your eyes move rapidly during stage four of sleep—hence the name REM, or rapid eye movement. Your eyes move side to side during this process, which may concern you if you’re viewing someone in this stage of sleep. It’s typically observable from the outside even though the eyes are closed.
Your Body
Despite your active eyes, the rest of your body—excluding your breathing muscles—freezes during this stage of sleep. This is so you don’t relay your dreams in the waking world. You’re essentially paralyzed, and this is responsible for the phenomenon known as sleep paralysis. Sleep paralysis occurs when your brain wakes up during REM sleep but your body stays still.
Your Brain
Unlike your body, your brain is highly active during this stage of sleep. Its activity levels are similar to when you’re awake.
Moving On From REM
You move on from REM sleep quickly at first. Your first REM cycle will usually only last 10 minutes. They get longer as the night goes on, eventually reaching up to an hour in length in some cases.
After stage two sleep, REM is the longest sleep cycle and you spend about a quarter of the night in this stage.
Waking Up During REM
You can easily wake up during REM sleep, and like deep sleep, you’ll be groggy and unrested.
How Often Does REM Sleep Occur?
The first REM cycle occurs after 90 minutes, and happen on a relatively regular basis. As stage two gets longer and stage three gets shorter you’re able to keep a decent balance and can assume you enter REM sleep after 90 minutes of NREM equally throughout the night.
Most people have 3–5 REM cycles per night.
Do We Dream During REM Sleep?
Although dreams can occur during any of the sleep stages-though in stage one they’re mostly hallucinations and in stage three they’re night terrors—you dream most vividly in REM sleep.
If you find yourself remembering a dream in extreme detail, you most likely weren’t far past your last REM cycle when you woke up.
REM is the period where your subconscious can dump everything out, show you your dreams and nightmares, as well as give you the opportunity to lucid dream.
Brain Waves During REM and Non-REM Sleep
It wasn't until 1953 that scientists discovered REM sleep, at which point machines were developed that were capable of monitoring brain activity as we slept, disproving the theory that all brain activity stopped during sleep.
They have also concluded that REM sleep is deeply linked to both learning and memory capacity, however, on the flip side, they found that a lack of REM sleep can help to lessen the impacts of clinical depression…but it is not yet understood why.
Brain Waves During the Sleep Cycle
| STAGE | FREQUENCY (HZ) |
AMPLITUDE (MICRO VOLTS) |
WAVEFORM TYPE |
|---|---|---|---|
| Awake | 15 - 50 | < 50 | |
| Pre-Sleep | 8 - 12 | 50 | alpha rhthym |
| 1 | 4 - 8 | 50 - 100 | theta |
| 2 | 4 - 15 | 50 - 150 | splindle waves |
| 3 | 1 - 4 | 100 - 200 | spindle waves and slow waves |
| REM | 15 - 30 | < 50 |
Do Sleep Cycles Change As You Get Older?
The information above primarily describes the experiences of adults—your sleep cycles haven’t always been the way they are.
Children's Sleep Cycles Into Adulthood
Newborn (0 - 4 Months)
There are only three sleep stages. Active is similar to REM sleep and is how infants are sleeping most of the time so they can easily wake for feeding. There are also quiet and intermediate sleep stages. There’s no distinct pattern to these sleep stages in infants.
Infants (4 - 12 Months)
Sleep patterns are becoming more concrete, with your typical four stages of sleep. This makes it easier to form a sleeping schedule through the night, with the inclusion of some daytime naps in light sleep.
Toddlers (1 - 3 Years)
Now the sleep patterns are more distinct than ever, but they don’t match that of an adult. Half of the sleep time is made up of an equal balance between stage three and REM sleep. Daytime naps are short and occur once daily, and most of it is spent in light sleep.
Pre-School (3 - 5 Years)
This period has sleep similar to the previous, except without the daytime nap. These young children still spend most of their time in deep sleep, sleeping about 9–10 hours throughout the night.
School Age (5 - 12 Years)
Older kids spend about a quarter of their time in deep sleep as it aids their development and growth. The standard is still 9–10 hours of sleep per night.
Adolescent (12 Years+)
Adolescents and teenagers sleep for about 30 minutes less than younger children, and they tend to go to sleep later due to their natural circadian rhythm. This causes the urge to sleep late in the mornings, but this desire goes away as the adolescent ages and the circadian rhythm shifts. There’s still a lot of time spent in deep sleep but it’s growing lesser as the sleep patterns morph to match that of an adult.
Elderly People
Elderly people retain their former sleeping cycles but spend less time in REM sleep.
What Else Can Influence Sleep Stages?
Outside of age, there are a few influencers that influence the sleep stages—except this time they disrupt healthy sleep.
Disorders
This one is obvious, but anyone with sleep disorders will have a disrupted and unhealthy sleep cycle due to frequent awakenings. Disorders include sleep apnea, insomnia, restless leg syndrome, and more.
Intoxication
A small glass of wine in the evening isn’t likely to disrupt your sleep, but the more alcohol you drink the bigger the disruption.
The alcohol inhibits your ability to go through REM sleep early in the night, so you may miss the first one or two REM sleep stages. However, as you sober up your body makes up for the missed REM sleep by spending more time in this stage.
If you’ve ever woken up from a night drinking with strong memories of odd, vivid dreams, this is the most likely culprit.
Recent Sleep Disruptions
If you’ve been getting too much, too little, or irregular sleep, your sleep cycles suffer. You may spend too long or too little time in the various sleep cycles, causing over-sleeping or having you wake up feeling unrested.
Sleep Stages - Final Thoughts
The four sleep stages are vital to your health and any disruption may impair your cognitive functions and physical health.
Avoid alcohol before bed, seek treatment for any sleep disorders, and try to stick with a regular sleep schedule. Remember:
- Stage one: Light sleep right after you drift off, 1–5 minutes.
- Stage two: Light sleep, your body relaxes, and it’s best to wake up during this stage.
- Stage three: Deep sleep, your brain, and body recover, you’ll wake up groggy.
- Stage four: REM sleep populated by vivid dreams and a feeling of unrest upon awakening.
If you have any questions or comments, we'd love to hear them below.
