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When You Fall Asleep

Diane Luke
Senior Editor, TipsHire

The ancient Greeks believed that sleep occurs when our brains fill with blood and when the blood is removed we wake up. Philosophers of the 19th century were thinking that sleep occurs when the mind is empty of thoughts. Even nowadays, sleep remains one of the greatest mysteries of medicine, because although we understand it better, we still have many questions that we can not answer. Dozens of clinical studies described the changes on the physical and mental levels that occur when you fall asleep, so, next, let’s see what really happens when you fall… asleep.

How does sleep work?

You spend one-third of your life sleeping, and the lack of sleep has an impact on your health, on both physical and mental levels. Long-term insomnia can destroy your body, mind, and social relationships, causing depression.

Doctors recommend about 8 hours of sleep per night, although the calculation is done differently, people needing one hour of sleep for every two hours they are awake.

The need for sleep varies from one species to another. If humans need 8 hours, the lions sleep for 13 hours a day, and squirrels and tigers need 14 hours. Instead, for an elephant 3 hours are enough, while 1 hour and a half of sleep are just enough for a giraffe.

Sleep is divided into several stages, which were identified in 1950. Our brain organizes the sleep process in four different stages, which are repeated cyclically every 90 minutes.

Sleeping stages

The first stage is the light sleep, in which if you suddenly wake up, you may not realize that you have fallen asleep.

In the second stage, some specific brain waves can be detected. Regular heartbeat and respiration and body temperature decreases can be observed during this second stage.

The third stage is considered deep sleep stage. The brain is emitting slower waves in the first part of this stage, and by the stage ends delta waves are emitted. If you wake up in this stage of sleep, you will feel disoriented. At this stage the blood pressure drops, breathing is slower, muscles relax and this stage is when your body recovers, charges with energy, and the tissues heal. Hormones are released, including the growth hormone, which is essential for children’s development.

The fourth stage, the last one, is the REM sleep in which rapid eye movements occur under closed eyelids. Now the brain is very active and dreaming occurs.

Sleep disorders

Scientists began to seriously study sleep since the ’70s and have so far identified more than 100 different sleep disorders. In addition to insomnia, which is manifested by difficulty in falling asleep and frequent awakenings from sleep, the most important categories of diseases are hypersomnia and parasomnia.


Called ‘sleeping sickness’, Narcolepsy is a form of hypersomnia, characterized by the excessive duration of sleep during the day and sometimes by sudden falling asleep for brief periods of time.

During these crises, patients go directly from wakefulness into REM sleep stage, leaping so other steps that are taken by the brain normally. An important role in this disease is played by a class of neuropeptides produced by the neurons in the hypothalamus.

Sometimes, narcolepsy is accompanied by a phenomenon which may frighten those attending such crises. The patient will experience sudden muscle weakness, sometimes so severe that person collapses to the ground paralyzed. This crisis is called cataplexy attack and is often triggered by strong emotions.

Other serious symptoms of narcolepsy and sleep paralysis hallucinations. Sleep paralysis occurs when the patient can not move nor can talk. The crisis usually occurs during the wake or sleep and can be frightening, especially if the affected person does not know what happens.

Sleep hallucinations are extremely unpleasant and somewhat resembles lucid dreams. They occur during the transition from sleep to wakefulness or vice versa.


Describes a wide range of sleep disorders, which many of them affecting mostly children (e.g. night terrors).

Nightmares fall under this category, too. It’s about dreams that are so frightening that a person suddenly wakes up scared.

Unlike nightmares, only a bad dream is not causing awakening. In adults, nightmares usually occur in the period of stress, illness, or post-traumatic stress.

Night terrors crisis occur in children around the age of 4 years and go away by themselves. During a seizure, the child cries and scream and keep the eyes open.

Unlike nightmares occurring during the REM sleep, night terrors are triggered in the third stage of sleep. An episode can last between one minute to 20 minutes and is accompanied by sweating, increased heart rate, and blood pressure. However, the child will wake up refreshed and with a good mental state.


This is another strange phenomenon of extreme danger. It is a form of parasomnia that occurs mostly in children and involves unconscious walking during deep sleep. About one-third of the children have an episode like this at least once, while only 4% of the adults face with this problem.

During the crisis, a person can go to the kitchen to eat, or can listen to music and when awaking will remember nothing. The episode can be triggered by a sudden noise or strong need to urinate.

To simply describes sleepwalking, is like the body wakes up, but the brain continues to sleep.

Somniloquy or sleep-talking

Sleep talking can occur in any stage of sleep.

The phrases could be understandable, but in other cases, the words could be completely meaningless and impossible to interpret.


This is a phenomenon very little understood, yet. When you fall asleep it manifests itself through gnashing of teeth during sleep, which can destroy the enamel and can cause jaw pain. Although half of the people move their jaws while they sleep, only 6% suffer from Bruxism.

People suffering from Bruxism can eliminate the negative effects on the teeth by using special dental guards (occlusal splints) that are mounted in the mouth and prevent tooth contact.

REM sleep disorder

This is the strangest phenomenon among all REM sleep disorders and it occurs in elder people, in particular. During REM sleep all muscles are paralyzed but in this sleeping disorder, muscles paralysis no longer appear and patients will walk, or act according to the dream they’re having at that time.

So this is like sleepwalking, only that in this case patients move as if their dreams are in fact reality. Therefore, these sleeping disorder episodes are very dangerous because people can hurt themselves or hurt others because sometimes patients think they are attacked and they tend to defend themselves.

People who have the brain region responsible for paralyzing muscles during REM sleep affected are most likely to develop this sleep disorder.

When you fall asleep the brain is not totally asleep

Although, apparently brain rests during sleep and does not maintain essential functions active, in reality, your brain work is very complex overnight.

Researchers noted that while sleep perceives stimuli not only complex, but the information assimilated in this period is used to make decisions, just as happens in the awake state.

Decision making

In an experiment, volunteers were asked to rank certain words in certain categories. Then, after they went to sleep were monitored by researchers. They noted that volunteers had a specific brain activity when these words were spoken as if their brains continue to work.

When they woke up, the participants no longer remembered the words heard during sleep, therefore the data processing was done unconsciously.

The finding suggests that sleep learning is possible, but research must continue to discover what kind of information can be treated as such.

The development and consolidation of memories

During both REM sleep and non-REM sleep, your brain consolidates new information received during the day and links it to the older information. Therefore, rest is important in learning because it helps record the new data to be easily remembered later.

Youngsters who spent a whole night learning before an exam will not achieve the desired results but on the contrary. A sleepless night will decrease the capacity of the brain to assimilate information by 40%.

Creative connections

When you fall asleep, your brain can make original and surprising connections that you can remember and use consciousness state, so sleep can be a good stimulus for creativity.

A study has shown that after a good night sleep, about 30% of the subjects have done new connections between seemingly unrelated ideas, leading to unexpected solutions for different problems.

Eliminating toxins

As indicated by several studies conducted in 2013, during sleep your brain has the mission ‘to clean up’. During the rest, molecules associated with neurological degeneration are eliminated. Thus, the space between neurons increases during sleep to allow any toxins to be eliminated in the waking state.

The lack of sleep causes toxins to accumulate in the brain and can lead to serious diseases such as Parkinson or Alzheimer, concluded a study conducted by the researchers of the University of Rochester.

Saving specific tasks

The brain stores new information in long-term memory using short pulses of high frequency that occur during the REM sleep. Usually, it is all about activities such as driving or playing tennis, which will eventually become an automatism.

When you fall… asleep!

Sure you know the feeling when you sit in bed when you fall asleep and suddenly you wake up having the feeling of falling and you are scared about it.

That trembling sensation that appears when you fall asleep is called, in scientific terms, ‘hypnagogic jerk‘.

In fact, what you’re feeling is only a muscle spasm that occurs in the hypnagogic state, which is when you are in that short period of transition between wakefulness and sleep. The spasm can occur spontaneously without any external cause or can be caused by noise, turning on a light, touch or other factors. Most times, this spasm is accompanied by the sensation of falling.

Hypnagogic spasm is a common phenomenon that affects almost everyone. Sometimes it happens during the night when you fall asleep but you won’t realize it happens because it’s not strong enough to wake you up.

No one knows exactly what causes the falling sensation, but there are several theories.

One of them says that this is a normal phenomenon, a small ‘misfire’ of the nervous system which is ‘confused’ during the transition between wakefulness and sleep.

Another theory explains falling sensation from the evolutionary point-of-view, saying that it could be a reflex inherited from our ancestors who slept in trees. When we fall asleep, our brain confuses the state of muscle relaxation to fall from a tree and reacting quickly through involuntary muscle contraction.

These being said, sleep is the body’s way to recharge its batteries and heal and is necessary to respect the medical recommendation for at least 8 hours of sleep per night in order to avoid health problems on physical and mental levels. On the other hand, when you fall asleep and ‘fall in sleep’ is a common muscles spasm and you shouldn’t worry about it but you should keep an eye on other disorders you might have and if anything is suspicious seek professional help.

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