5 Sleep Stages Explained

Until new research came about in the 1950s, scientists thought our bodies were mostly dormant during sleep. But as it turns out, our brain is pretty active during this time. Research also found that there are distinct stages we go through while we’re sleeping. Learn more about these stages and what your body is up to during each one.

Sleep Stage 1 This is the lightest stage of sleep. During this phase, you might drift in and out of sleep or awaken easily. Meanwhile, your muscle activity and eye movements start slowing down.

Sleep Stage 2 The second sleep stage involves slower brain waves (the fluctuations of electrical activity in the brain) with occasional bursts of rapid waves. Eye movements stop during this stage.

Sleep Stage 3 During stage 3, brain waves slow way, way down to essentially the slowest rate (also known as “delta waves”). There are some smaller, faster waves occasionally detected during this phase.

Sleep Stage 4 In stage 4, your brain almost exclusively produces delta waves. During both stages 3 and 4, it’s very difficult to wake someone up. Generally, these are known as the “deep sleep” stages. No eye movement or muscle activity takes place during this time.

REM Sleep The REM (rapid eye movement) stage first occurs about an hour to 90 minutes after falling asleep, with additional periods of REM sleep usually occurring throughout the night as you cycle through these stages. During REM sleep, breathing typically becomes shallow and irregular and the eyes exhibit sudden, jerking motions. Heart rate and blood pressure tend to increase and limb muscles become temporarily paralyzed. Many people experience vivid dreams during this stage. Ideally, your body will naturally cycle through these sleep stages through the night. Creating a comfortable sleep environment will help avoid being awoken during one of the stages, which can contribute to poor sleep quality. Remember that good rest is important for your physical, mental and emotional health!