Sleep is a vital activity, accounting for about 30% of each person's day, helping to restore physical and mental well-being after hard work. You may not know that even when you are in a deep sleep, your body is not completely asleep but continues to perform vital activities. So, do you know how to tell if someone is in a deep sleep? What are the main stages of sleep and what do they mean? Let's explore this useful information in Ru9's article below.

1. Understanding the stages of sleep

To understand how to tell if someone is in a deep sleep, you need to clearly understand the stages of a normal sleep and their meanings. Accordingly, sleep usually consists of 5 main stages: drowsiness, light sleep, deep sleep, very deep sleep, and finally REM sleep (also known as dream sleep). These stages always occur in sequence and repeat throughout your sleep.

 Sleep is divided into different stages.

In addition, the 5 stages of sleep are also divided into 2 main parts: NREM/Non-REM sleep (non-rapid eye movement) which includes drowsiness, light sleep, deep sleep, very deep sleep, and REM sleep (rapid eye movement) which includes dream sleep. 

Drowsiness stage 

The drowsiness stage usually lasts only 3 to 15 minutes, starting from when you close your eyes to sleep. In this stage, you are often in a light sleep and can be easily awakened. Many people wake up in this stage, some may experience sudden jerks (also known as Hypnic Myoclonia), similar to the startled reaction when someone taps your shoulder.

Light sleep stage

Typically, this stage lasts for about 50% of the entire night's sleep, during which the eyes stop moving and brain activity also slows down. Additionally, the brain at this time also experiences rapid, sparse waves in the next stage.

Deep sleep stage

Studies show that the deep sleep stage lasts only about 10% of sleep time. At this time, brain waves are slow and sparse, but sometimes interspersed with a few rapid waves. During this deep sleep stage, breathing rate, heart rate, and body temperature all decrease, and muscles relax.

Very deep sleep stage

As one of the most important parts, the very deep sleep stage accounts for about 20% of the entire sleep, and is also the time when the body is completely at rest. Therefore, factors such as heart rate, breathing rate, and temperature will drop to their lowest levels, eyes will not move, and limb muscles will be completely relaxed. 

If you are accidentally woken up during this stage, you will feel extremely dizzy, disoriented, and return to normal in a few minutes. When you observe these signs, it also means you have learned how to recognize someone in a deep sleep.

Observing sleep behavior is a way to tell if someone is in a deep sleep. 

Dream sleep stage

The dream sleep stage is completely separate from other stages and is called REM, or Rapid Eye Movement, accounting for approximately 20% of the total sleep duration. Except for inactive limb muscles, the breathing rate, heart rate, temperature, and frequency of eyeball movements all gradually increase during this stage. This is also the stage where dreams appear, and you may still remember some of them upon waking.

2. What are the signs of a deep sleeper?

Have you ever wondered how to tell if someone is in a deep sleep? Start by observing their seemingly inexplicable activities, because at this time, the part of the brain that controls activities and perception is entering a resting phase.

Decreased heart rate and breathing rate

The easiest way to tell if someone is in a deep sleep is that their heart rate and breathing rate are typically slower when they're asleep. The reason for the decreased rate is that the body and brain are relaxing to recover energy.

Unresponsive to light and sound

When in a deep sleep, the senses are significantly less sensitive, so stimuli from the sleeping environment, such as sound or light, will be harder to wake them up.

Less repositioning and movement

To tell if someone is in a deep sleep, observe how often they change positions. If they lie still and don't move much, it's highly likely they are in a deep sleep. Furthermore, if their eyelids show no movement and their body is completely relaxed, that's also a sign of deep sleep.

Talking in their sleep while in a deep sleep

One way to tell if someone is in a deep sleep is to hear them talk in their sleep. According to a recent accurate report, about 5% of adults experience this condition of sleep-talking, and it usually occurs about 1-2 hours after falling asleep.

 Talking in one's sleep is a sign of someone being in a deep sleep.

Specifically, the part of the brain that manages speech remains active, leading to involuntary mouth movements and sleep-talking. This is a common phenomenon and has been proven to be harmless to the body.

Flailing arms and legs

Although rare, sometimes when the body enters a state of deep sleep, you may easily flail your arms and legs. Experts explain that this is caused by a limb movement disorder, which is only found in about 4% of people, especially women. 

If you suffer from this syndrome, you may act very strangely while sleeping and remember nothing when you wake up, with cycles of 20-40 seconds. Usually, this syndrome is caused by the use of harmful foods, heart disease, musculoskeletal disease, or overwork. You can easily recognize someone in a deep sleep through the information provided by Ru9. 

Falling in a dream

Many people have admitted that they fell in a dream and felt so dizzy that they woke up startled. This syndrome is also known as "myoclonic jerks" and can occur in people of all ages. It can be said that falling in dreams causes heart rate, breathing rate, and even temperature to increase rapidly, even causing sweating and shock.

Flailing arms and legs is also a way to tell if someone is in a deep sleep. 

Currently, there is no definitive answer to explain the cause of this phenomenon. However, most people often believe that prolonged insomnia and stress can lead to a lack of coordination between the body and brain, causing imbalance and indirectly creating "falls" in dreams. However, this is also a common way to tell if someone is in a deep sleep.

See more: How to sleep soundly even with noise around

In short, Ru9 has shown you a few easy and common ways to tell if someone is in a deep sleep, which is through their characteristic actions during sleep. During deep sleep, some organs of the body perform necessary activities. That's why many experts recommend deep sleep to protect our health in the long run. 

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