The 4 stages of sleep: NREM, REM, and your sleep cycle
Clinically reviewed by Dr. Chris Mosunic, PhD, RD, CDCES, MBA
Learn about the 4 stages of sleep, how long each cycle is, and how much deep sleep you really need. Plus, what occurs during each stage, including REM and NREM.
Sleep is a vital part of our daily routine. It impacts our health, mood, and overall wellbeing. There are several stages of sleep, and each plays an important role in helping us get the rest we need.
What is a sleep cycle?
A sleep cycle is a series of stages that our brain and body go through during sleep. Each cycle can be broken down into two primary types of sleep: non-rapid eye movement (NREM) and rapid eye movement (REM).
NREM sleep: This includes three stages, each progressively deeper than the last. NREM sleep is characterized by slower brain waves, reduced heart rate, and relaxed muscles. It's during NREM sleep that our body repairs tissues, builds bone and muscle, and strengthens the immune system.
REM sleep: Following NREM sleep, we enter REM sleep. This is a deep sleep phase, but our brain waves are as active in REM sleep as when we're awake. REM sleep is important for cognitive functions such as memory consolidation, learning, and emotional processing.
Each sleep cycle lasts about 90 to 110 minutes, and adults usually go through four to six cycles per night. The proportion of NREM to REM sleep changes as the night progresses, with more NREM sleep occurring in the first half of the night and more REM sleep in the second half.
Understanding your sleep cycles can help you recognize the importance of both quantity and quality of sleep. A good night's sleep means ensuring these cycles are uninterrupted and complete, allowing your body and mind to benefit fully from each stage of sleep.
The 4 stages of sleep
Each stage of sleep plays an important role in our overall health. The multiple sleep cycles help us spend adequate time in each stage for the best possible wellbeing.
1. NREM 1
The initial stage of sleep, often considered the transition phase between wakefulness and sleep, NREM 1 is a light sleep stage where you can be easily awakened. Muscle activity slows, and the eyes move slowly under the eyelids. Some people experience a falling sensation or sudden muscle contractions known as hypnic jerks. Typically, this stage lasts about 5-10 minutes.
2. NREM 2
In this stage of sleep, your body goes into a more subdued state. Heart rate and body temperature decrease, eye movements stop, and brain waves become slower with occasional bursts of rapid waves known as sleep spindles. NREM 2 is a period of light sleep before we enter deeper sleep, and it lasts approximately 10-25 minutes during the first sleep cycle, extending during later cycles. About 45-55% of an adult’s nightly sleep is spent in this stage.
3. NREM 3
Often referred to as deep sleep or slow-wave sleep, this stage is what helps us feel refreshed in the morning. During NREM 3, brain waves slow and are known as delta waves. It's the hardest stage to wake up from, and if awakened, you might feel disoriented for a few minutes. This stage is essential for restorative processes like tissue repair, muscle growth, immune system strengthening, and memory consolidation. As the night progresses, the duration of NREM 3 decreases. It makes up about 15-25% of sleep in adults.
4. REM sleep
The final stage of the cycle is where dreaming occurs. REM sleep is characterized by rapid eye movements, increased brain activity, and temporary muscle paralysis, which prevents us from acting out our dreams as they’re happening. During REM, the brain processes information and emotions from the day, playing a vital role in learning and memory. In adults, REM sleep makes up about 20-25% of the sleep cycle. The final REM stage is the longest, lasting up to an hour.
What interferes with your sleep cycle and sleep stages?
Various factors can disrupt your sleep cycle, affecting the quality and duration of each sleep stage. Simple changes in habits and environment can make a significant difference in improving your sleep quality.
Stress and anxiety: Emotional stress can lead to increased brain activity, making it difficult to fall asleep and stay asleep.
Lifestyle choices: Drinking caffeine or alcohol, especially in the hours before bedtime, can significantly impact sleep. Caffeine can delay the timing of your body clock and reduce the total sleep time. Alcohol can lead to non-restful sleep and frequent awakenings later in the night.
Sleep environment: A disruptive sleep environment, such as a room that's too hot, too cold, too noisy, or too bright, can prevent you from falling asleep or reaching the deeper stages of sleep. Comfortable bedding and a quiet, dark, and cool environment can promote better sleep.
Irregular sleep schedules: Inconsistent sleep and wake times can throw off your body's internal clock or circadian rhythm. This can make it difficult to fall asleep and wake up when you want, and can also affect the quality of sleep.
Health issues and medications: Certain health conditions like sleep apnea, chronic pain, or acid reflux can disrupt sleep. Some medications may also interfere with sleep.
Age-related changes: Changes in sleep patterns and sleep architecture are common with aging. Older adults may spend less time in deep sleep and REM stages and can experience more awakenings.
Diet and exercise: Heavy meals close to bedtime can lead to discomfort and indigestion, affecting sleep quality. Lack of regular exercise can also contribute to poor sleep, as physical activity helps to regulate sleep patterns and promote deeper sleep.
Use of electronic devices: The blue light emitted by phones, tablets, and computers can suppress the production of melatonin, the hormone that regulates sleep, making it harder to fall asleep.
10 ways to get more deep sleep at night
Improving deep sleep is essential for your overall health and wellbeing. Good sleep habits can significantly improve the quality of your deep sleep, leaving you feeling more refreshed and alert during the day.
1. Establish a consistent sleep schedule
Going to bed and waking up at the same time every day, even on weekends, can help regulate your body's internal clock. Make your sleep schedule consistent to help you transition smoothly between different stages of sleep.
💙 The Power of Rest is a Calm series dedicated to the importance of rest.
2. Create a relaxing bedtime routine
Engage in calming evening activities, like reading a book, taking a warm bath, or practicing relaxation techniques to signal to your body that it's time to sleep.
💙Jay Shetty’s Gratitude Body Scan for Sleep can help you wind down with a sense of gratitude for your body.
3. Optimize your sleep environment
Keep the room dark, quiet, and cool. Consider using blackout curtains, earplugs, or a white noise machine.
4. Reduce exposure to screens
Blue light emitted from phones, tablets, and computers can interfere with melatonin production. Try to avoid these screens for at least an hour before bedtime.
5. Choose your meals mindfully
Avoid heavy or large meals, caffeine, and alcohol before bedtime. These can disrupt your sleep cycle, especially the deep sleep stages.
💙 The Mindful Eating series can help you establish a more mindful relationship with food at all times of day.
6. Incorporate regular movement
Physical activity during the day can help you fall asleep more easily at night and deepen your sleep. However, try not to exercise too close to bedtime as it might keep you awake.
7. Manage stress and anxiety
Use techniques such as deep breathing, meditation, or gentle yoga to help calm the mind.
💙 This Soften Into Sleep meditation can help you relax and release tension before bed.
8. Choose the right bed
A comfortable bed can make a significant difference in your sleep quality. Ensure your mattress and pillow are suitable for your sleeping position and personal preferences.
9. Avoid long or irregular napping
While short power naps can be beneficial, long or irregular napping can negatively affect your nighttime sleep, especially your deep sleep stages.
💙 The Refreshing Nap Sleep Story is timed to help you drift off to sleep and wake back up in order to get back to your day.
10. Seek professional help if needed
If you often struggle with sleep, talk to a healthcare provider to identify any underlying issues and get appropriate treatment or guidance.
Stages of sleep FAQs
What are the 4 stages of the sleep cycle?
The four stages of sleep are part of our natural sleep cycle, each with unique characteristics.
NREM 1: The first stage is a light sleep, where you drift in and out of sleep. It's easy to wake up from this stage, and it typically lasts 5-10 minutes.
NREM 2: This involves a deeper level of sleep. You become less aware of your surroundings, your body temperature drops, and your heart rate slows. This accounts for the largest portion of your sleep cycle.
NREM 3: This deep sleep stage is crucial for feeling refreshed. It's difficult to wake up from, and is important for physical recovery and growth.
REM sleep: Characterized by rapid eye movement, the final stage is when most dreaming occurs. It's essential for cognitive functions like memory, learning, and emotional processing.
Which is better: REM or deep sleep?
Both REM and deep sleep are essential for different reasons. REM sleep, which is rich in dreams and brain activity, is important for processing emotions and consolidating memories. Deep sleep is important for physical recovery, tissue repair, and immune system strengthening. Each stage serves a unique and vital purpose. They’re complementary and both necessary for overall health.
What is the most restful stage of sleep?
The most restful stage of sleep is NREM 3, the deep sleep stage. During this stage, the body is in its most relaxed state, with the lowest heart rate and blood pressure. It's the hardest stage to wake up from, and interruption of this stage often leads to feeling groggy or disoriented. This stage is key for physical rejuvenation and recovery.
Is REM sleep the deepest?
The deepest stage of sleep in terms of physical relaxation is NREM 3. However, REM sleep is deep in a different sense. It's when the brain is highly active, processing information, consolidating memories, and engaging in vivid dreaming.
How many hours of REM sleep do you need?
On average, adults typically require about one to two hours of REM sleep per night, accounting for about 20-25% of total sleep. Achieving sufficient, good quality REM sleep is important for cognitive and emotional health.
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