What Happens While You Sleep? The 4 Sleep Phases Explained

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Wondering whether you’re getting enough sleep? You may be turning to your smartphone or another wearable device to find the answer. Many devices record your heart rate, movement and hours slept. But this data may not describe your whole sleep experience.

“Devices and sleep apps offer a snapshot of what happens when you sleep. But they don’t present the whole picture. The best measure of your sleep quality is how you feel as you go through the day,” says Cynthia Fellman-Couture, RN, a sleep research coordinator at Henry Ford Health. “If you’ve gotten quality sleep, you’ll feel re-energized and ready to take on the day.”

Here Fellman-Couture dives into your sleep cycle, explaining what happens at each stage. She also shares tips for improving your sleep and when to see your doctor for difficulty sleeping.

What Are The Different Phases Of Sleep?

Each night you cycle through four stages of sleep. A full cycle through all sleep stages initially lasts one and a half to two hours. If you sleep for the recommended seven to eight hours at night, you may cycle through each stage three to five times.

Here’s what happens in each sleep phase:

  • Stage 1: This stage typically lasts up to five minutes. Your heartbeat and breathing slows, and your muscles relax. But your brain remains active as you settle into sleep.
  • Stage 2: You enter a light sleep, with your brain activity slowing and body temperature dropping. Early in the night, this stage will last for up to 30 minutes, and then shorten to 15 minutes or less in later sleep cycles. You’ll spend the most time — 45% to 55% — in this stage.
  • Stage 3: You get your deepest, most restorative sleep in this stage. Your muscles relax, and your heartbeat and breathing slow to their lowest levels. Your body restores energy and performs tissue growth and repair during this stage. At the beginning of the night, you may spend up to 44 minutes in stage 3, with shorter periods later in the night.
  • REM (rapid eye movement): Your brain is most active in this stage, generating dreams. Your eyes move rapidly as you dream, but your body becomes paralyzed, preventing you from acting out images. Research shows that this stage may also help process and store information you’ve learned. After REM sleep, you’ll return to stage 1 to kick off the next sleep cycle.

Fellman-Couture explains that many people are surprised at how sleep cycles impact their nighttime rest:

  • Periodic awakenings occur between sleep cycles: It’s normal to wake up or briefly arouse and change sleep positions during the night, especially between sleep cycles.
  • You’re more likely to remember dreams from later REM sleep: You’ll experience more REM sleep in the latter part of the night. You’re most likely to remember dreams from these later REM stages when you wake.
  • It’s okay to take time to fall asleep: While some people can fall asleep soon after their head hits the pillow, others may take up to 30 minutes to fall asleep. It’s okay if you can’t fall asleep immediately.
  • The best sleep occurs during the first half of the night: Sleep stages 2 and 3, which offer the best sleep, are longer during the first half of your nighttime rest. As the night wears on, you spend less time in these stages and more time in REM sleep.

Tips For Getting A Good Night’s Sleep

Some people are sensitive sleepers and react to any changes in their sleep environment. Others can fall and stay asleep amidst interruptions. But Fellman-Couture says everyone can benefit from good sleep habits, which include:

  • Avoiding alcohol before bedtime: Alcohol disrupts sleep. While you may feel drowsy after drinking alcohol, it can cause shallower sleep and more awakenings during the night.
  • Preparing your mind and body for sleep: Take time to wind down. Turn off electronics. Practice meditation or relaxation techniques to calm your mind. Sleep in a cool, dark, quiet room to help you fall and stay asleep.
  • Sticking to a regular sleep schedule: Go to sleep and wake up at the same time every day. Sleeping in on the weekend can interfere with your sleep that night.
  • Limiting beverages before bedtime: It’s essential to stay hydrated during the day. But if you tend to wake up to use the bathroom at night, stop drinking several hours before bed. Most people also need to stop drinking caffeine at least six hours before bed to get quality sleep.

When To See A Doctor About Sleep Problems

“There’s no need to suffer if you’re having difficulty sleeping. Your doctor or a sleep specialist can pinpoint the cause of your poor sleep,” says Fellman-Couture. “And you often don’t have to go to a sleep lab for overnight testing. Newer at-home wearable testing devices track sleep in the comfort of your bed.”

She recommends contacting your doctor if you experience:

  • Daytime fatigue that interferes with work, school or family activities
  • Frequent nighttime awakenings and difficulty falling back asleep
  • Snoring or breathlessness at night, which may be symptoms of sleep apnea where your airway becomes blocked

Many treatments are available for insomnia and other sleep disorders, including lifestyle changes, behavioral therapy and prescription medications.


To find a doctor or sleep specialist at Henry Ford, visit henryford.com or call 1-800-436-7936.

Cynthia Fellman-Couture, RN, BSN, PhD, is a sleep research coordinator in the Thomas Roth Sleep Disorders Center at Henry Ford Health.

Categories: FeelWell