Most of all, it's when you sleep that the brain stores your day's experiences, primes your memory, and releases hormones that regulate energy, mood, and mental acuity. And the brain completes all this activity in about 7 to 8 hours. Moreover, to understand why it takes so long, it's necessary to understand how sleep works.

Sleep Stages

First and foremost, sleep has two parts: Rapid Eye Movement (REM) sleep and Non-REM (NREM) sleep. Furthermore, NREM sleep has 3 stages: Stage 1, Stage 2, and Stage 3. Moreover, both NREM and REM sleep together occur in cycles that are repeated every 90 to 110 minutes. For example, one complete cycle would be Stage 1 sleep, followed by Stage 2 sleep, followed by Stage 3 sleep, and finally REM sleep. And, each of these sleep stages can last anywhere from 5 to 15 minutes. Because one complete cycle takes about 90 minutes, the brain does about 5 sleep cycles over a period of 450 minutesor 7.5 hours.

Above all, the first half of the night is essentially NREM sleep where the REM stagesare short. And the second half of the night is essentially REM sleep where the NREM stages are short.

Stage 1

Stage 1 occurs soon after you fall asleep. Within minutes, the brain produces alpha and theta waves. This stage lasts anywhere from one to ten minutes. And, because you are only sleeping lightly, you can quickly return to being fully awake.

Stage 2

This stage lasts about 20 minutes. In this sleep stage, your heart rate slows down and your body temperature drops. In addition, the brain produces sudden increases in brain wave frequency known as sleep spindles. Also, the senses are blocked making it difficult to be awakened. Finally, your body decreases its activity in preparation for going into Stage 3 or slow wave sleep.

Stage 3 or Slow Wave Sleep

Most noteworthy, slow-wave (also known as delta waves) sleep is the deepest phase of NREM sleep. And slow-wave sleep occurs in stage 3 (which, here, also includes what some call stage 4).In fact, dreaming and sleepwalking occurs when the brain is in slow-wave sleep. And slow-wave sleep is important because that is the time when the brain consolidates memory. In addition, this is the sleep stage when the body repairs muscles and tissues, stimulates growth and development, and boosts immune functions. Also,slow-wave sleep is the most restorative to your body. As a result, interruptions in slow-wave sleep are the most damaging to your metabolic health.

nrem rem sleep stages

REM Sleep

REM sleep is associated with creativity. It's also when most of the dreaming occurs. Generally, you enter this stage about 90 minutes after first falling asleep. Also, this stage can last up to an hour.

Moreover, in this stage, the brain becomes very active. In fact, the heart rate and blood pressure increases, and breathing becomes irregular, shallow, and fast.

Also, the Very Big Brain website points out that this phase plays an important role in learning and memory function. Indeed, this is the stage when the brain consolidates and processes information from the previous day for storage in long-term memory.

Finally, the duration of REM sleep starts short in the first sleep cycle when you first fall asleep and gets longer with ensuing sleep cycles.

Why Should You Care

First, if you are an insomniac, the frequent waking up or taking a long time to fall asleep, means your sleep cycles either get disrupted or you don't enough complete sleep cycles during the night.As a result, you don't get all the benefits from the restorative effects of sleep.

Next, if you have sleep apnea, your sleep gets disturbed, when you gasp for air. As a result, you don't get enough deep sleep.

woman sleeping

Also, if you have REM sleep at the beginning of the night, you may be suffering from narcolepsy. While someone with excessive REM sleep might be suffering from depression.

Meanwhile, not getting enough sleep consistently means you don't get enough REM sleep. As a result, your REM sleep starts earlier and earlier.

Or, if you wake up too early in the morning, you are cutting short your REM sleep, which, as noted earlier, is longest just before your normal wake up time.As a result, you lose the benefits of a full REM cycle.

Finally, if you a late sleeper, you may not get the full benefits of slow wave sleep or by not getting the benefits of full five sleep cycles.


Because the full benefits of sleep occur over about eight hours, it is important to get that amount of sleep. Moreover, regular sleep deprivation, prevents your brain from fully restoring itself, which severely impacts your health.

Meanwhile, physical activity improves sleep by reducing stress and tiring you out. Also, many kinds of afternoon workouts help reset the sleep wake cycle by raising body temperature slightly, then, allowing it to drop and trigger sleepiness a few hours later.