The Five Stages Of Sleep

By Tiffany Tseng. May 7th 2016

Do you ever wonder what happens when your brain is “resting” at night? Why are some nights full of dreams, while others have none? How come you sometimes still feel exhausted after sleeping? Understanding the sleep cycle as well as the stages of sleep may help answer some of these questions.

The Importance Of Sleep

The typical adolescent needs around 8.5 hours of uninterrupted sleep every night to perform at his or her maximum the next day. As a person ages, however, the number of hours may vary to as little as 6 hours per night, depending on the individual. During this restful time, our bodies physically repairs itself, strengths the immune system, replenish lost energy, and regulate hormones. Uninterrupted, normalized sleep is crucial for a healthy individual to function properly.

The 5 Stages Of Sleep

There are a total of 5 stages in the sleeping cycle. The first four stages are classified as NREM (non-rapid eye movement) sleep, while the last stage is classified as REM (rapid eye movement) sleep. NREM sleep comprises 75 percent of one night’s sleep, while REM only takes part of the remaining 25 percent.

Stage I

During Stage I, people prepare themselves for sleep by first drifting through Alpha phase, then Theta phase. Alpha phase is similar to that of daydreaming, and is the phase where meditation of the brain takes place. Your body then enters Theta phase, the area between being awake and falling asleep. At this time, it is normal to have muscle contractions and twitching of the body that may bring you back to Alpha phase; it is a sign that the body is starting to relax. The average person spends about seven minutes in Stage I of the sleeping cycle, or light sleep.

Stage II

In Stage II, which lasts about 20 minutes, the body temperature drops lower. The heart also beats slower as the breath steadies. The brain starts to send short, rapid signals known as Sleep Spindles to help the body and mind disengage from the surroundings. At this time, a cool room would be helpful to aid a better sleep.

Stage III

Stage III is the transitional phase between light sleep and deep sleep. The brain begins to send Delta waves throughout the body.

Stage IV

By Stage IV, the delta waves are in full bloom, and this deep sleep lasts for about 30 minutes. This is a very deep and restorative sleep where the body starts to replenish itself from the day’s work. For growing teenagers or for body builders hoping to build muscle, this is the stage of sleep where tissue growth and repair takes place. Hormones are also released to balance the body and reduce stress. The muscles are fully relaxed, breathing becomes slower, and energy is restored to the body.

Sleep nuisances such as bed wetting or sleepwalking may occur at this stage of sleep. Usually, children can grow out of such habits, but if it becomes a recurring problem, be sure to see a doctor for proper remedies.

Stage V

Stage V sleep is commonly referred to as REM sleep or Paradoxical sleep. The latter name refers to the fact that while this is the deepest stage of sleep, it paradoxically has the most brain activity compared to the first four stages. Most of the dreams occur during this time, along with a burst in brain activity. If you look at a sleeping person and see that rapid eye movement has taken place, it means that the person is dreaming. Cortisol, the stress hormone, also dips at an all-time low to promote maximum energy conservation.

Furthermore, the whole body becomes immobilized as the muscles shut off, making this stage of sleep the deepest and hardest to wake up from. In fact, if a person is awoken during REM sleep, he or she will feel exceptionally groggy, sluggish, and confused compared to being woken up in other stages of sleep. Dreams during REM sleep are also harder to wake up from. This self-paralyzing mechanism during REM sleep is explained as a protective measure to ensure the body gets as much deep sleep as possible. This stage usually occurs 90 minutes into sleep.


Generally, the stages happen in order when you first go to bed. However, after the first session of REM sleep, the body may skip erratically throughout the other stages of sleep, only to return to REM sleep once more. While the first REM sleep is the shortest, it gets longer each time your mind dips back to Stage V. People typically experience 4 to 5 sessions of REM sleep every night.

Now that you understand your sleep cycle better, be sure to hit the sack every night and get a sufficient amount of rest, especially REM sleep!


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