Sleep 101: The Sleep Stages And What Impacts Them

Everyone sleeps. Different people may have different sleep patterns, but scientists have identified specific stages of sleep that are natural and beneficial to all humans. 

These sleep stages generally happen in an orderly way unless something happens to disrupt them. Knowing more about your stages of sleep each night can help you sleep better and function better in your waking hours.

This article will explore the stages and effects of sleep deprivation. We’ll also discuss potential causes of poor sleep quality and a lack of sleep, including disorders like sleep apnea. 

General effects of sleep deprivation 

Sleep deprivation has significant short-term and long-term effects on overall health and well-being. In the short term, lack of total sleep can make it difficult to fall asleep and stay asleep, leading to daytime fatigue and impaired cognitive function. Long-term sleep deprivation weakens the immune system, increasing susceptibility to illnesses and chronic health conditions.

Most adults need at least seven hours of sleep to maintain health according to the National Sleep Foundation. 

What is a sleep stage?

A sleep stage outlines separate processes that occur in the body during each sleep period. One step follows another until a complete sleep cycle is over, and another one begins. 

If all goes well, we wake up from this time of mental activity after several sleep cycles, refreshed and ready to start the day.

How many stages of sleep are there?

There are five stages in a healthy sleep cycle: stage one, stage two, stage three, stage four, and REM sleep. However, some sources refer to the first four sleep stages as non-REM sleep (or NREM sleep) and mention the REM stage separately from them.

Scientists have studied the five sleep stages extensively. Often, they agree on a basic description for each stage. Sleep progresses naturally from stage one through stage four and REM sleep. 

When one cycle of sleep ends, another one follows unless you awaken. On a typical night, you may spend 50% of the night in stage 2 sleep, 20% in REM sleep, and the rest of your sleep time in the other stages. However, sleep medicine, sleep habits, or other factors could affect the time spent in each state.

Stage 1

Stage one is a period of light sleep that happens when you first fall asleep. Moments of awareness may be interspersed between moments of light sleep. You may also see brief or incomplete images during this stage. 

During stage one, you may awaken quickly. Your eyes may move, but only slowly. Muscle activity can diminish, although you may jerk awake easily if you're disturbed by environmental stimuli.

Stage 2

In stage two of the sleep cycle, you can fall from a light sleep into a slightly deeper sleep. Your eyes stop moving. Brain activity slows, except for occasional rapid brain waves called sleep spindles.

Stage 3

Stage three sleep, also called slow wave sleep, is the beginning of deep sleep. Prolonged brain waves, called delta waves, arrive. Fast brain waves are also occasionally present. You may not have awareness or dreams during this stage. This stage is thought to be critical for body recovery and boosting your immune system. 

Stage 4

In stage four sleep, the faster brain waves disappear nearly completely. The predominant or only brain waves present are the slow delta waves. Your eyes and muscles don't move, and it can be more challenging to wake up for any reason. 

If you do wake up directly from stage three or four sleep, you may feel sluggish and disoriented for a few minutes before you fully wake.  

Stages three and four, the deep sleep stages, are when children most commonly wet their beds, have night terrors, or sleepwalk. Although it is rarer, adults may have the same problems during the deep sleep stages.

REM sleep

Rapid eye movement sleep, or REM sleep, is the phase of sleep in which most dreams and nightmares happen. This stage gets its name from the fast, jerky movements of our eyes during this phase. 

Your breathing speeds up and becomes shallower and more irregular. Your heart rate and blood pressure increase to levels like those of wakefulness. You may not be able to move your arms and legs during this phase, which can keep you from acting out the dreams physically.

Some individuals may experience sleep disorders during this phase, such as sleepwalking, night terrors, or sleep paralysis.

How do the sleep stages progress?

What can disrupt your sleep stages cycle?

Various environmental stimuli may bring you out of sleep at any stage. You may hear a noise, such as a car horn or loud music. You may see a flash of light even though your eyes are closed. Smells can awaken you if they're strong enough.

Certain substances, like drugs or alcohol, may also disrupt your sleep or cause sleep problems. For example, people who use nicotine may experience symptoms of insomnia (difficulty falling asleep) and disturbed sleep. Some prescription medications can also affect sleep. Sleep disorders such as obstructive sleep apnea could also cause a person to wake up during early sleep stages, preventing them from entering deep sleep cycles or REM sleep. More than 40 million Americans experience sleep disorders that can also cause sleep deprivation.

If you are struggling with substance use, contact the SAMHSA National Helpline at (800) 662-4357 to receive support and resources. Support is available 24/7.

What happens when each of the stages of sleep are disrupted?

Whether you experience severe effects on your health can depend on how much sleep you're losing and if you’re living with short-term or prolonged sleep deprivation, but it may also depend on what sleep stage is being disrupted.

Stage 1 and stage 2

It is not uncommon to awaken during stage one or two, as these are often the lighter stages of sleep. People generally tend to fall back to sleep relatively quickly if awakened during these stages. The main problem with being awakened during stage one or two sleep is that you may not pass into deeper sleep if these stages are continually disrupted, and your sleep quality may suffer.

Stages 3 and 4

Most of the time we spend in the deep sleep of stages three and four happens long before we wake. In these stages, the body repairs and renews itself, so disruptions may affect your overall health.

When you are first awakened from these stages, you might feel groggy and have trouble remembering where you are. If you must get up and go somewhere, you may have to wait to wake up more thoroughly before you can drive safely.

REM sleep

Being awakened during REM sleep may also have profound effects. Notably, when people are awakened suddenly from REM sleep, their self-image suffers. If it happens often enough, it can lead to mood disorders.

Ways to track your sleep stages

Concerns about your sleep can be distressing, especially if you have daytime symptoms of sleep deprivation caused by problems with your sleep stages like daytime sleepiness, impaired memory, or disordered thinking. 

One step you might take is to track your sleep stages to find out how much time you're spending in each and the overall quality of your sleep during the night. There are a few different ways to do this.

Smart device sleep tracking

Many apps and electronic devices have been developed to track sleep. Generally, these devices track when sleep stages occur if you wear the device while sleeping. When you awake, you can see how long you slept and how long you spent in light, deep, and REM sleep.

Tracking sleep stages in a sleep lab

If sleep deprivation or disruption becomes a severe physical or mental health concern, your doctor may send you to a sleep lab for a sleep study. At most sleep studies, you are connected to monitoring devices by leads that attach to your head, body, and monitoring equipment. 

With this advanced equipment, the technicians can see readouts that show details of your sleep stages. They may then report to your healthcare provider, who can take appropriate measures to improve your sleep.

Using a sleep stage chart

You, sleep lab technicians, or your doctor may make a sleep stages chart from the information gleaned from a sleep study or electronic device. 

The information on the stages of the sleep chart might all seem academic at first. However, when you look at it carefully, you may see when disruptions occurred. You can tell briefly if any stages of sleep are missing or if you are getting very little of one of the sleep stages. 

The chart can be helpful for your doctor as well because they can use it to identify a potential sleep disorder and determine what treatments might be most effective for you to prevent sleep deprivation. A psychologist may also refer to the sleep chart to help you find practical techniques for better and enough quality sleep.

What are the sleep deprivation stages?

Sleep deprivation stages are defined by the number of hours you've been awake. The following stages of sleep deprivation can help you understand some of the things that happen to you as sleep deprivation continues and you become more and more sleep-deprived.

After 24 hours 

After 24 hours of sleep deprivation, coordination, memory, and judgment may be impaired.

After 36 hours 

At 36 hours, without sleep,

 inflammation in your body can increase, which may cause heart disease or high blood pressure. Your hormones can also be affected. The earlier effects on coordination, memory, and judgment become more severe.

After 48 hours 

At 48 hours, you may become disoriented and have involuntary microsleeps, potentially without realizing it.

After 72 hours 

At 72 hours, you may hallucinate easily and frequently. Your cognitive processes can be seriously affected in several ways, making every situation more difficult to understand and manage.

How to solve problems resulting from disturbed stages of sleep

Sleep cycle disturbances may impact your physical and mental health. If you're experiencing sleep cycle disturbances, it can help to speak with a medical doctor. 

Depending on the type of disturbances you're experiencing, you may choose to see your primary care physician, a sleep specialist, or your psychiatrist for support. 

If you've only experienced mild issues with sleep, you may begin to resolve them before they become more serious. A psychologist or therapist can help you develop new strategies to get to sleep and stay asleep for the recommended seven to nine hours. 

Online therapy for concerns with sleep and chronic sleep deprivation

Online therapy may benefit you if you're tired or don't want to leave home to meet with a counselor. Many individuals enjoy meeting with their therapist at home because studies show that most people feel most comfortable at home. 

A therapist may help you identify the changes you need to make to your sleeping environment and routine. Research indicates that Cognitive Behavioral Therapy (CBT) is an effective treatment for sleep disorders like insomnia. CBT for sleep disturbances is usually a structured program where a therapist will help you identify and change behaviors that could impede your sleep.

Through online platforms like BetterHelp, you can get matched with a licensed therapist online to start working on your sleep patterns and concerns.