What Are the Sleep Stages?

Everyone loves to sleep. It would be hard for most people to make it through the day without it. However, while you are asleep, your body does not simply take a vacation. Instead, your body cycles through four stages that serve specific purposes to get you ready for your next day’s activities.

When the lights go out, it’s time for your body to get ready for sleep. But you might be surprised to learn that the active cycle of sleep actually starts with stage 1 of slumber. As you pass into this phase, also known as somnolence, various changes occur in your muscles and brain waves begin to slow.

Once you turn out the lights, your body’s sleep cycle is only just beginning. Learn what you need to know about the stages of sleeping.

Sleeping may seem passive, but your body works in four stages while you’re peacefully asleep in your bed. Learn about the different sleep stages and how the normal sleep cycle works.

What Is a Sleep Cycle?

Most of us know we need enough sleep to stay healthy and do our best at work. And the National Sleep Foundation recommends about 7–9 hours of sleep each night for adults. But most people don’t understand how your brain “resets” itself by going through a series of sleep cycles when you go to sleep each night, which was once thought to be just a period of inactivity.

A baby’s sleep cycle lasts about an hour and a half, while a teenager’s takes around ninety minutes to complete. Each of these stages is characterized by different physical and mental states of activity, consciousness, and hormones. Understanding these sleep stages is important because if your sleep cycle is interrupted (such as by an external disturbance such as light, or an internal one like alcohol consumption), it can affect you deeply.

A complete cycle of sleep stages lasts about an hour and forty minutes, but your entire sleep cycle can be as short as a few hours, or extend into several days. When it comes to children, the sleep cycles are much shorter, lasting only a few hours, while for adults the cycles can last up to 2 days.

The first three stages of sleep are classified as non-REM sleep, and the final stage is Rapid Eye Movement (REM) sleep.

Stage 1 of the sleep cycle is the first part of sleeping which can easily be disturbed by anything that makes noise or any sudden movement. It normally takes about 7 minutes to enter this stage and once you do it’s quite easy to wake up.

Stage 2 sleep begins about 20 minutes after falling asleep and usually lasts about 20 minutes. In this phase, the sleeper is more difficult to awaken. Breathing slows and heart rate decreases further. Muscle contraction decreases and the body temperature drops slightly. Brain waves become slower with high amounts of activity in the theta and alpha wavelengths. This is a great time to practice breathing exercises that will help you develop your overall health, achieve better sleeping habits, or simply relax more when you’re trying to drift off to sleep.

This is the stage where slow wave sleep occurs, where the brain produces slower delta waves and the sleeper does not move his/her eyes or muscles. As the brain produces even more delta waves, sleepers enter a deep sleep stage from which it is difficult to wake up. This stage of deep sleep helps you feel refreshed in the morning. It is also a time of muscle repair and regeneration, growth and development, and improved immunity.

Within 90 minutes after falling asleep, you enter Rapid Eye Movement sleep, which is named so for the way your eyes rapidly move back and forth behind your eyelids. REM sleep is thought to contribute to the development of the central nervous system in infants, which may explain why infants need more REM sleep than adults. This sleep pattern is characterized by dreaming since your brain is very active during this stage. Physically, you experience faster and irregular breathing, an increased heart rate, and an increase in blood pressure, but your arm and leg muscles are temporarily paralyzed, stopping you from acting out your dreams. The REM sleep stage becomes longer and longer with each cycle of sleep, starting at about ten minutes during the first cycle and lasting an hour in the final sleep cycle. This sleep stage is crucial for learning, memory, daytime concentration, and mood.

The deep sleep stages of Stage 3 and REM sleep have unique benefits. An average adult needs one to two hours of deep sleep per night to feel healthy and feel restored. If you wake up tired frequently, it could be that you are not sleeping deeply enough; this phase is crucial in helping you learn and feel your best. Discuss this with your doctor if you don’t feel like you are getting the restful sleep that you need.