4 Stages Of Sleep - Why It Matters

In scientific terms, sleep is a state of altered brain activity. During non-REM sleep, brain activity looks very different than it does when you're awake, but during the REM portion of your snooze, it actually looks very similar to an awake state. In all stages, though, there's a lot going on.

“Sleep, in a way, is still a big mystery to us,” says Michelle Drerup, PsyD, Director of Behavioral Sleep Medicine at Cleveland Clinic. “We know that in non-REM sleep and when there’s deep sleep, there’s physical restoration occurring, but in REM sleep, there’s still some debate. It is thought that we’re filing things away from the day and [engaging in] memory consolidation.” 

During sleep, there are also distinct physical changes in the body, such as changes in eye movement and muscular tension. Further variations in electrical activity in the brain show when each stage of sleep begins and ends. And speaking of those stages, there are four of them, plus the REM phase, and we cycle through them about four to five times each night if we’re getting a proper amount of shut-eye.

Sleep stage 1

Our breathing and heartbeat become regular, our muscles relax, and our body temperature falls. We become less aware of external stimuli, and our consciousness starts to withdraw from reality. The slightest noise is enough to wake you from this stage, and if you do indeed wake up, you might think you haven’t been asleep at all. You have likely experienced the sensation of falling suddenly, typical of this stage, and some people also experience twitching. Sleep stage 1 can last from five to 10 minutes, according to Cleveland Clinic.

Sleep stage 2

Sleep becomes deeper during this stage, and our muscles relax further. Physical sensations are dampened significantly, and our eyes do not move. Electrical activity in the brain occurs at a lower frequency than when we’re awake. About half of our total sleeping time is spent in stage 2, which means that we’re spending more of our repeated sleep cycles in this stage than in any of the others, according to the National Institute of Neurological Disorders and Stroke. Stages 1 and 2 are known as the light-sleep phase. Together, they last for about 20 to 30 minutes per sleep cycle. We return to stage 2 several times during the night.

If you’re going to take a power nap, it is generally recommended that you wake up during this second stage of sleep. “A 15- or 20-minute nap tends to be really refreshing for people because your brain activity is not into the slow-wave activity of stage 3,” says Drerup. “When you go into that type of sleep, it's much more difficult to wake, you’re groggy, and you have sleep inertia.”

Sleep stages 3 and 4

We reach the first of our deep-sleep stages, stage 3, after approximately 20 to 30 minutes, and the second, stage 4, after about 45 minutes. At that point, the body is completely relaxed, and we are more or less completely disconnected from reality. If you want to wake someone from deep sleep, you need to make a lot of noise or shake them quite hard. Waking someone from stage 4 is almost impossible—a bit like trying to wake a hibernating bear in the middle of winter. This is the most restful part of the night’s sleep. Muscular activity decreases even further, and our eyes do not move. Stages 3 and 4 make up about 20 percent of our time asleep, but this proportion decreases as we get older. Here's how you can combat America's sleep-deprivation crisis—and get more shut-eye.

Article by Readers Digest
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