Key Points
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There are four stages of sleep, which you normally cycle through six or eight times a night.
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Disruption of the four stages of sleep causes many health problems.
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Learn some tips for keeping your sleep cycles healthy.
Sleeping seems like it should be simple enough, but some nights of sleep are surprisingly eventful. Maybe you wake up a few times during the night for no apparent reason, have strange dreams, or even talk or walk in your sleep without realizing it. You may have also found that these sleep patterns change with age.
To understand what happens when you sleep — and whether it's anything to worry about — you need to understand the stages of sleep. All of them are necessary for good sleep, but there are ways they can go wrong.
How Many Stages of Sleep Are There?
Some online sources say there are four stages of sleep, while others claim there are five. However, they're the same stages; the five-stage systems just count "awake" as the first stage.
What Are the Four Stages of Sleep?
The first three stages of sleep are the non-rapid-eye-movement (NREM) stages. The last one is the rapid-eye-movement (REM) stage.
Stage One
The first stage of sleep is the lightest and shortest. It's the state popularly called "nodding off" — you're starting to lose consciousness but are not fully relaxed or oblivious to your surroundings. Someone in this state is easy to wake up, but if undisturbed, stage one lasts for one to seven minutes before stage two begins.
Stage Two
In stage two, you are asleep, with the deep, slow breathing everyone recognizes. Your heart rate also slows down, and your body temperature drops. However, some movement continues: if your dentist has warned that you're grinding your teeth at night, that's when it happens.
Exciting changes in your brain activity also happen during this stage. Sleep spindles — neurons firing in short, powerful bursts — and long delta waves called K-complexes characterize this stage. Researchers believe both play a role in consolidating your memories, which seems to be one of the primary functions of sleep.
Stage Three
The third stage of sleep is also called slow-wave sleep due to its slow brain-wave patterns. This is the deepest sleep; someone in stage three is difficult to wake up and will be fuzzy-headed for up to an hour, a state called sleep inertia.
Stage three sleep is when your body repairs and regrows tissues most intensively.
Stage Four
Stage four is also known as rapid-eye-movement sleep because the sleeper's eyes jerk around under their closed lids. Breathing also gets more erratic during this stage, and sometimes random muscles twitch. The brain waves get much faster and are similar to wakefulness. This all happens when you have your most vivid dreams.
You might think you don't dream, but you almost certainly do; you just don't remember it. Even people who remember their dreams usually only remember what they were dreaming of right before they woke up.
How Long Do the Four Stages of Sleep Last?
The length of the four stages of sleep depends partly on age. In newborns, the four-stage cycle has not yet developed, which is why infants' sleep is so erratic. As children age, their sleep cycle lengthens while their total sleep time decreases, from 15 to 18 hours in infancy to about eight hours in adulthood.
The typical adult sleep pattern goes like this: a few minutes of stage one, 10 to 25 minutes of stage two, 20 to 40 minutes of stage three, and 10 to 60 minutes of stage four. Then the pattern repeats six or seven times, although it will often just cycle between two, three, and four. Stages two and four get longer with each cycle, while stage three shortens.
All this varies with the individual, however. If your sleep doesn't follow the typical pattern, that does not necessarily mean something is wrong, so long as you have no negative symptoms. However, bad things can happen if you don't go through the stages of sleep properly.
What Happens if You Don't Go Through All of Them?
While researchers are still working to understand all the purposes of the sleep stages, it's clear that they all have benefits. Processing and consolidating memories happens throughout stages two through four. Stage three is essential for physical healing and recovery because that's when your body focuses on tissue repair.
REM sleep might not seem beneficial if it gives you weird dreams, but research indicates that the weirdness helps your creativity. Moreover, a severe lack of REM sleep can set your brain into daytime dreaming — also known as hallucinating.
"Getting enough quality sleep on a regular basis can help to prevent anxiety, depression, and suicidal thoughts," Soaak CEO Henry Penix recently told Snooze. "Poor sleeping habits can also lead to paranoia and delusions. In extreme cases, sleep deprivation can even trigger psychotic episodes."
Even if it doesn't get that bad, lack of sleep can aggravate mental problems that you already have, such as anxiety, depression, obsessive-compulsive disorder, and post-traumatic stress syndrome. It can also tire you and slow down your mental acuity and reflexes.
How the Stages of Sleep Can Go Wrong
Messed-up sleep cycles indicate that you have an underlying condition or need to change something in your behavior or environment. There are many possibilities if you suspect something is wrong with your sleep.
Sleep Apnea
Sleep apnea is a condition that obstructs breathing during sleep. People who snore are more likely to have it since both sleep apnea and snoring result from the soft tissues of the throat collapsing and obstructing the airway.
Sleep apnea stops breathing entirely for a few seconds, interfering with sleep because it sets off the sleeper's alarm bells that they need air. As a result, sleepers get less stage three and stage four sleep than they should and often suffer from symptoms like fatigue, mental fuzziness, depression, anxiety, and similar problems.
There are multiple risk factors for sleep apnea. Sometimes behavioral factors like overeating and alcohol consumption are to blame. However, sometimes it's just due to the shape of your mouth and throat, which you can assess using the Mallampati score.
If you suspect you have sleep apnea, ask your doctor to give you an at-home test to provide a diagnosis. Various treatment methods are available, so follow your physician's advice.
Walking and Talking in Your Sleep
Walking and talking in your sleep occurs during stages three or four. Stage three sleepwalking is more common in children than adults because it results from an imperfectly developed sleep cycle, so the sleeper might try to do things they'd normally do during the day, like dressing, eating, or going to the bathroom. This is usually harmless and resolves itself with time.
REM sleep disorder causes people in stage four to act out their dreams. Given how scary many dreams are, this can be very dangerous. Consult a physician if your family or bed partner says you're acting bizarrely while asleep.
Narcolepsy
People with narcolepsy can, like infants, plunge right from waking to stage four sleep. As a result, their sleep can come in sudden, brief episodes, even while they're in the midst of an activity. This prevents them from getting enough stage three sleep, though, so they're also chronically tired.
Talk to your doctor if you suspect you have narcolepsy because there are medications to treat it.
Restless Legs Syndrome
Restless Legs Syndrome (RLS) is often found in older people, although it occasionally appears during pregnancy. Sufferers have a strong urge to move their legs while sitting down, often egged on by crawling, aching, or itching sensations. This affliction most often hits at night, so it understandably interferes with quality sleep.
The cause of RLS is unknown, but it's sometimes connected to iron deficiency (especially in women), so a round of iron supplements might do the trick. If that doesn't work, consult your doctor, who can prescribe drugs that might help.
Alcohol
Alcohol is a sneaky bastard when it comes to sleep: it can help you fall asleep but mess up your sleep stages. That's because when its relaxing effect wears off, your body gets a burst of energy, and you wake up or move to a lighter sleep stage. That's why people tend to sleep for so long after drinking: it's not until the effects wear off that they can get to stages three and four.
However, if you don't have extra time to sleep, limit alcohol consumption before bed.
Medications
Medications can hinder your sleep cycle in different ways. Some are stimulants, which prevent you from reaching the deeper stages, while others are sedatives and bring the same risks as alcohol. However, there are some medications, like antidepressants, that aren't known for either but can still interfere with your sleep in more subtle ways.
If your doctor prescribes you a drug for long-term use, ask if it might affect your sleep and what you can do about it.
Temperature
As you go through the stages of sleep, your core body temperature gradually drops, reaching its coldest point at stage four. Sleepiness makes most people feel chilly and want to curl up in a cozy place, which is a common urge of mammals. This warmth helps the muscles relax, and the blood vessels expand, lowering body temperature.
Cold can keep you awake by preventing your body from relaxing. On the other hand, heat can also keep you awake because the perception of temperature is a meaningful way your body knows what time of day or night it is. For most of human history, the air temperature around the sleeper would drop throughout the night and then start to lift again when the sun rose, so the primary signals are cold equals sleep and warmth equals wake. Modern bedrooms, however, tend to retain their temperature all night, which can disturb sleep cycles.
According to the Cleveland Clinic, the ideal bedroom temperature is between 60 and 67 degrees, which will vary with the individual. If that seems too cold when you go to bed, you might try layering the bedclothes so that you have the ability to throw them off as you get warmer during the night. Conversely, if you live in a warm climate and don't have or don't want air conditioning, there are also special cooling mattresses you might investigate.
How To Get Your Best Sleep
When it comes down to it, if you don't have an underlying sleep disorder, anything that interferes with your comfort during the night can interfere with healthy sleep cycles.
Some tips for maintaining healthy sleep:
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Give yourself plenty of time to sleep. Sleep's cyclical nature means waking up at night is common, especially as you age. That's not inherently a problem, but you do need to give yourself enough time in bed to cover the gaps.
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Choose your beds, bedding, and related accessories carefully. Check out Snooze's reviews of the latest products to find the right bedding for your body and sleeping positions.
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Find the right temperature for your bedroom, which might be cooler than you think. If you live in a quiet place, opening the window connects you to the natural nighttime temperature cycle.
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Turn off unneeded lights as you near bedtime. Darkness is another signal to your body that it's time for sleep.
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Avoid eating heavily or drinking alcohol too close to bedtime.
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Develop a relaxing routine to help you wind down. This can be anything that helps you feel calmer: meditation, a warm bath, prayer, light reading, crossword puzzles, or anything else that mellows you out.
Enjoy Your Sleep in All Its Stages
Good sleep is critical to mental and physical health. When you understand how sleep cycles work, you're better prepared to provide your body and mind with the rest you need. With great sleep, you're ready to take on the world!
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