At night we’d like to sleep peacefully and restore energy. Nevertheless, it is difficult to find a person who has never encountered some strange and unpleasant sensations accompanying sleep.

Bright Side decided to tell you about such experiences, which remain a mystery for science to this day.

Sleep paralysis

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How it feels: The person wakes up at night and cannot move. Added to this are frightening hallucinations and a feeling that there is someone else in the room. In antiquity, this state was associated with mischiefs of evil spirits.

Why it happens: Normally, when we fall asleep, we are paralyzed so that we don’t sleepwalk and such. With sleep paralysis, our muscles “turn off” when the brain is awake.

Approximately 7% of the population have experienced sleep paralysis at least once (source). They say this is more likely when sleeping on the back.

Hypnagogic hallucinations

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Why it happens: This is one of a few types of hallucination that mentally healthy people may have. Children have them more often (source), which could be the reason they don’t want to go to sleep. Such hallucinations may be due to stress or simply a good imagination. They can also appear if you go to bed drunk.

Sleep talking

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Why it happens: Men and children are more prone to this (source), and the reason is stress. The person’s psyche is trying to resist what he or she does not agree with in reality.

A dream within a dream

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Why it happens: Esotericists believe that if you have such a dream, this indicates your predisposition to spiritual practices. Official science can’t explain why this happens.

Sleepwalking

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Why it happens: Somnambulism occurs in about 4.6-10.3% of the population, with children affected more often (source). The cause is still unknown, as are methods of treatment.

Exploding head syndrome

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Why it happens: This happens when, for some reason, there is a surge of neural activity in the areas of the brain responsible for processing sound (source). Sometimes the syndrome is coupled with insomnia or jet lag.

Sleep apnea

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Why it happens: During sleep, the pharynx muscles relax, which sometimes leads to blockage of the airways. Obesity, smoking, and old age increase the risk. Fun fact in a world of anxiety: one may alleviate it by playing the didgeridoo, an Australian wind instrument (source).

Recurring dreams

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Why it happens: Psychologists believe our brain uses such dreams to pay attention to something we didn’t notice in our daily life. These stories will return until the situation is resolved (source).

Falling onto the bed

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Why it happens: Sleeping is similar to dying — the heartbeat and breathing slow down, muscle tone is reduced. The brain “gets frightened,” perceives this as a real death, and checks whether the person is alive, sending impulses to the muscles.

Out-of-body experience

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Why it happens: The phenomenon is very difficult to study. While scientists know that the illusion of getting out of the body does exist, it is not clear how it works and why it arises. It’s also unclear how to deal with this. Yet some know how to enter this state deliberately. They do so to expand the boundaries of their cognitive capabilities.

Sudden enlightenment during sleep

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Dmitri Mendeleev, a Russian chemist, was obsessed with creating a periodic table of elements — and then he saw it in a dream. Something similar happened with the chemist August Kekulé when he dreamed of a formula for benzene.

Why it happens: Sometimes our subconscious already knows the answer, although it has not yet reached consciousness. During sleep, the subconscious is more active and could provide the insight. Sleep is great, but sometimes it comes with even more perks.