Recognize the 4 stages of sleep: from "chicken sleep" to deep sleep & bull; hello healthy

You may have heard that while sleeping, you go through a series of stages. But, what does that really mean? Isn't sleep just… sleep? Eits, wait a minute. In fact, there are still many things passing through your brain while you are asleep. Why so?

We now know that the brain is very active during sleep. Sleep is not just an inactive and passive part of our entire daily life cycle. Recording electroencephalograph Nathaniel Kleitman and Eugene Aserinksy's (EEG) shows that sleep actually consists of different stages that occur in a characteristic sequence.

The normal cycle of sleep and wakefulness implies that many nervous systems are activated, while others are turned off. Research has also shown that a chemical called adenosine builds up in our blood when we are awake and causes drowsiness. This chemical compound will then gradually break down by itself when we sleep.

During sleep, we usually go through four stages of sleep from Non-REM sleep (NREM) and REM sleep, aka Rapid Eye Movement. The sleep cycle starts from stage 1 of NREM to REM sleep, then returns to stage 1. We spend nearly 50 percent of our total sleep time in stage 2 of NREM sleep, about 20 percent in REM sleep, and the remaining 30 percent in other stages. Babies, in contrast, spend about half of their sleep time in REM sleep.

Recognize the four stages of sleep

There are three stages of Non-REM sleep. Each stage can last from five to 15 minutes. You will go through a total of four years before finally reaching the REM sleep phase. Dreams usually occur during REM sleep.

Stage 1 NREM: Chicken naps

During the first stage of sleep, which is light sleep, your body, mentality, and mind are on the threshold of reality and subconsciousness — semi-conscious, half (almost) asleep. The brain produces what are known as beta waves which are small and fast. Your eyes are closed, but you can still easily wake up or wake up. Eye movement at this stage is very slow, as is muscle activity.

As the brain begins to relax and its performance slows down, the brain also produces slow waves called alpha waves at the same time. During this period of sleep, you may experience strange but very real sensations, known as hypnagogic hallucinations. Common examples of this phenomenon include feeling like falling or hearing someone call your name. Familiar, right?

Another very common event that occurs during this period is known as a myoclonic jolt. If you have been suddenly shocked without any reason, it means that you are experiencing this phenomenon. It may seem alarming, but myoclonic jolt is actually quite common.

Then, the brain produces high-amplitude theta waves, which are very slow brain waves. People who wake up from stage 1 sleep often remember shards of memory visual images. If you wake someone up during this stage, they may report that they are not really asleep.

Stage 2 NREM: Welcoming a deep sleep

Heart rate and breathing slow down, become more regular, and body temperature decreases. You will also become less aware of your surroundings. If a sound is heard at this stage, you cannot understand what the content is.

When entering the second stage of sleep, eye motion stops and brain waves slow down, in the presence of occasional bursts of fast waves, called sleep spindles. In addition, stage 2 NREM sleep is also characterized by the presence of a K-complex, i.e. a short negative high voltage peak. These two phenomena work together to protect sleep and suppress responses to external stimuli, as well as to aid in the incorporation of sleep-based memory and information processing. Our bodies get ready for deep sleep.

Because you can skip this stage several times throughout the night, there is more time spent in the second stage of sleep than at any other stage, and usually accounts for 45-50% of the total sleep time for adults, even young adults.

Stage 3 NREM: Sleep well

The third stage of sleep is what is called deep sleep. At this stage, the brain releases delta waves, which are initially punctuated by smaller, faster waves, and will then be exclusively dominated by delta waves. During this stage, you become less responsive and sounds and activities in the environment may fail to generate a response. No eye movement or muscle activity. The third stage also acts as a transitional period between light sleep and deep sleep.

It would be very difficult to wake someone who was soundly asleep. Usually, if he wakes up, he is not able to adjust to the changes as soon as possible and often feels groggy and confused for a few minutes after waking up. Some children experience bed-wetting, night terrors, or sleepwalking during the deep sleep stages.

During the deep sleep stage, the body initiates tissue repair and regrowth, builds bone and muscle strength, increases blood supply to muscles, improves and strengthens the immune system. Energy is also restored and growth hormone - essential for growth and development, including muscle development.

REM sleep: dreaming sleep

When we switch to REM (Rapid Eye Movement) sleep, our breathing becomes faster, irregular, and shallow; the eyes move in all directions very quickly, as if restless; increased brain activity; and, heart rate increases, blood pressure rises, and, for men, develops an erection. Most dreams start at this stage

The American Sleep Foundation states that people spend about 20 percent of their total sleep at this stage. REM sleep is also often referred to as the sleep paradox, because while the brain and other body systems are actively working, the muscles relax. Dreams occur as a result of increased brain activity, but muscles experience temporary, deliberate paralysis.

The first period of REM sleep usually occurs about 70 to 90 minutes after we fall asleep. A complete sleep cycle takes 90 to 110 minutes on average. After about 10 minutes in REM sleep, the brain usually cycles back through the non-REM sleep stages. On average, four additional periods of REM sleep occurred, each of which was longer in duration.

The first sleep cycle each night contains relatively short REM periods and periods of deep sleep. As the night progresses, the REM sleep periods increase in duration, while the fullness of sleep decreases. In the morning, people spend nearly all of their time asleep in stages 1, 2, and REM sleep.

You will lose some of the ability to regulate your body temperature while under REM sleep, so hot or cold temperatures that are hot or cold in your sleeping environment can disrupt your sleep.

It's also important to understand that you don't go through all of these sleep stages in sequence. Sleep starts at stage 1 and advances to stage 2, and then 3. After sleep stage 3, stage 2 sleep is repeated before entering REM sleep. After REM sleep ends, the body usually returns to stage 2. If REM sleep is disturbed, our body does not follow the development of the normal sleep cycle, so the next moment we fall asleep. Conversely, we often slip straight into the REM sleep stage and have REM periods that are prolonged until we "catch up" at this stage of sleep.