For most people, the word "sleep" is synonymous with calm and relaxation after a long day. In fact, in this unconscious state, the body undergoes a multitude of changes. It meticulously removes the damage it has sustained and prepares for the new day, constantly sorting, restoring, and renewing. So every time you wake up "as a different person," consider how close to the truth this expression is.

 1. Storing and sorting memories

People are restless creatures. We're constantly going somewhere, doing something, and communicating with someone, all while simultaneously storing away memories. But a file is useless if it can't be found. Anyone with a cluttered desktop knows this.

During sleep, the brain replays, catalogs, and stores events, discarding all unnecessary information. The preservation of long-term memories plays a crucial role in a person's ability to function normally. Long-term memory is essentially unlimited, so vivid memories are sure to stay with you for years to come.

Sometimes we recall scenes from childhood more easily than events from the previous week. This is a trick of the memory, which is responsible for learning and storing the most useful information. Its main activity occurs during the deep phase of slow-wave sleep, which is comparable to the brain's daytime activity. As consciousness transitions to rest, the brain switches to a mode that stabilizes the most important life memories, allowing for their rapid recall when needed.

2. Lowering temperature and blood pressure

Half an hour before sleep, the body lowers its body temperature. This is done to slow down the metabolism and avoid nighttime hunger. As a result, the heart rate slows and blood pressure drops. Temperature also drops to 35.6 degrees Celsius, just 1 degree below hypothermia. There's no risk of freezing while sleeping, as the body requires less energy.

After waking up, blood pressure and heart rate accelerate to match the energy expended. However, a temporary imbalance occurs, leading to mental fogginess and lethargy—typical symptoms upon awakening.

3. Paralysis

Remember those nightmares where you can't run, scream, or move? Well, this phenomenon ("sleep paralysis"), while terrifying, is quite natural. During sleep, the brain blocks neurotransmitters and muscle receptors, effectively paralyzing the entire body. Sometimes this happens during the initial stages of sleep or upon awakening, when consciousness is clear but movement is impossible.

Due to its eeriness, this condition has become the basis for many myths and legends inextricably linked to hallucinations. In these legends, immobilized people are visited by demons or similar mythical monsters (from characters from Anglo-Saxon legends to creatures from Chinese folklore).

4. Stretching

During the day, gravity and compression of the vertebrae place pressure on the spine. This causes the fluid in the spinal disc to shift, causing a decrease in height of approximately 1 cm by evening. When the back is recumbent, the fluid returns, increasing height by the same amount.

Although the difference of 1 cm is small, the release of stress also allows for growth during sleep. In fact, growth is only possible during sleep. This is due to both the relief of spinal pressure and the predominantly nocturnal production of growth hormones.

5. Sleepwalking

Not everyone suffers from it, but almost one-third of the population has experienced it at least once in their life. Technically, sleepwalking is a sleep disorder in which the brain, on the brink of unconsciousness, performs difficult tasks, such as getting out of bed, going to the kitchen, and even driving.

Sleepwalking is a disturbing phenomenon, but it is quite common, especially among children. Friends, parents, and roommates of sleepwalkers note their dazed and confused state during bizarre activities (such as cooking), only after which they are able to return to bed.

Scientists are still unsure why people sleepwalk. Some experiments have suggested that genetics may be to blame. Sleepwalking often occurs during slow-wave sleep, when the brain processes memories from the day.

This may explain the short-term memory deficits of sleepwalkers. When they wake up in the morning, they can't recall a single moment of their nighttime adventures.

6. Spasms

When we fall asleep, our body twitches. Every time. As mentioned above, during sleep, the body often becomes paralyzed to prevent us from moving while awake during dreams. But there is one moment when we are neither asleep nor awake.

It's a kind of hypnotic sleep. It's believed to be a delay in the "relax" signal being sent from the brain to the nervous system. How exactly this works isn't fully understood. Some scientists believe it's a relic of a primitive reflex that misinterprets falling asleep as suddenly landing from a tree.

Regardless of the cause, hypnotic sleep is further evidence of complex unconscious processes. We experience them while essentially awake. Sometimes, it can be so powerful that it leads to awakening.

7. The brain uses more energy

The bulk of the energy produced during wakefulness (approximately 80%) is used for physical activity, breathing, and speaking. During sleep, these activities are not performed, so the excess energy is sent directly to the brain.

This means that the brain consumes even more energy during certain stages of sleep than during daytime activity. Sleep is the brain's proper time, a kind of leisure time during which it streamlines the processes that enable it to perform energy-intensive tasks and make complex decisions during the day.

8. We lose weight in our sleep.

Have you ever woken up with a throbbing thirst? This is due to the evaporation of about 0.5 liters of water during the night. The air inside the lungs is quite warm (about 36.7 degrees Celsius) and humid. The average room temperature is below 36.7 degrees Celsius, so the cold airflow you inhale constricts the lungs and draws moisture from the body. About 0.02 grams of water is lost during a single breath. Over the course of the night, about half a liter is lost.

Carbon has a similar, but less powerful, effect. Everyone knows that we inhale oxygen (2 atoms) and exhale carbon dioxide (3 atoms). When we breathe out one more atom than we take in, the mass decreases.

As a result, about 0.7 kg of mass is lost during each night's rest. The same processes occur during the day, but the carbon and moisture are replenished by drinking and eating food.

9. Brain cleansing

While awake, toxins and other waste products are deposited in the cells of the body and brain. Before sleep, the body shuts down, and the brain springs into action. Essentially, it opens a valve, allowing cerebrospinal fluid to flow from the spinal cord to the brain to cleanse the body and detoxify toxic waste.

This process is part of a more complex cycle called cellular respiration. It's a series of reactions that improves cells' ability to regenerate energy from food and maintain overall body function. The toxins eliminated during sleep are a residual effect of this process.

Although this cleansing affects the entire body, its effects are most noticeable in the brain, where the effects of inadequate sleep are felt. Brain clutter is one of the main causes of a bad mood after a long, healthy night's sleep.

10. Dreams

Dreams, an integral part of every human life, are also worth mentioning. However, even today, scientists cannot fully explain this phenomenon. So the question of "Why do we dream?" remains unanswered.

If you try to recall the plots of your dreams, they seem downright implausible. Every night, the brain creates an imaginary world that exists only in the mind, but we perceive it as entirely real. Upon awakening, almost all traces of this imaginary reality disappear. It may sound strange, but dreams are taken for granted, comparable to brushing your teeth or going to work.

While the true meaning of dreams remains a mystery, the processes associated with them are still understood: strengthening long-term memory, eliminating brain toxins, enhancing alertness, and so on.

But this question is not new. The true purpose of dreams has fascinated humans for millennia, as evidenced by the works of the ancient Greeks and Egyptians. Despite advances in technology and advances in science, theories about the origins of this mysterious phenomenon remain just that—theories.

11. Sleep paralysis

A person wakes up at night unable to move. This is accompanied by frightening hallucinations and the sensation that there is a stranger in the room. In ancient times, this condition was associated with the machinations of evil spirits. Normally, when we fall asleep, we are paralyzed to prevent us from performing actions in our sleep. During sleep paralysis, our muscles "switch off" while the brain is still or already awake. Approximately 7% of the population has experienced sleep paralysis at least once (fact). It is said to occur more often when sleeping on your back.

12. Hypnagogic hallucinations

When a person hovers on the fine line between sleep and wakefulness, they, while conscious, see uncontrollable images before their eyes. Often, these are scary faces and fantastical creatures. This is one of the few types of hallucinations experienced by mentally healthy people. Children (in fact) commonly experience them, and this can be the reason they don't want to go to sleep. Such hallucinations are often caused by stress or simply by those with a strong imagination. They can also occur if you go to bed drunk.

 13. Sleep Talking

Usually, a person suffering from somniloquy (sleep talking) is unaware of it. This condition is completely harmless psychologically. Perhaps the person with this problem worries about spilling the beans. Somniloquy is more common in men and children (fact). The cause is the notorious stress. The person's psyche tries to resist something they disagree with in reality.

14. A dream within a dream

A person dreams, then wakes up, but strange things continue to happen to them. It turns out they simply dreamed they woke up. The theme of such dreams was explored in the film "Inception." It later emerged that many people have experienced similar experiences. Esotericists believe that having such a dream indicates a predisposition to spiritual practices. But mainstream science cannot explain why this happens.

 15. Somnambulism

This condition is the opposite of sleep paralysis—consciousness remains asleep, but muscle paralysis does not occur. While asleep, people can walk, clean, or even leave the house, which is often very dangerous. The next morning, people remember nothing. Somnambulism occurs in approximately 4.6–10.3 percent of the population, with children being the most affected (fact). The cause of sleepwalking remains unknown, as are treatments.

16. Exploding head syndrome

A person awakens from a loud explosion or bang. Sometimes it seems as if the sound was so loud that it could cause deafness. It may be accompanied by a growing hum or flash. The phenomenon is not dangerous, but it causes fear in people; some believe they are having a stroke. For some reason, there is a surge of neural activity in the areas of the brain responsible for processing sound (fact). Sometimes the syndrome occurs due to insomnia or jet lag during long-haul flights.

17. Sleep apnea

Sleep apnea is a sudden cessation of breathing during sleep. This causes the person to awaken. Sleep quality declines, the brain experiences oxygen deprivation, and it becomes difficult to get a good night's rest. During an attack, blood pressure fluctuates, which can cause heart problems. During sleep, the muscles of the throat relax, which in some people leads to airway obstruction. Those at risk include the obese, smokers, and the elderly. Incidentally, playing the didgeridoo, an Australian flute, can help with apnea.

18. Recurring dreams

Weird dreams that repeatedly replay the same plot have probably occurred to everyone. Psychologists believe that the brain uses such dreams to draw our attention to events we're not consciously aware of. These plots will recur until the situation is resolved (fact).

19. Falling into bed

Sometimes we feel as if we've been thrown from a height onto our bed, and we startle and wake up. Sometimes, before this, we dream of flying or stumbling and falling—a rather unpleasant sensation. The dream state is somewhat reminiscent of death—the heartbeat and breathing slow down, and muscle tone decreases. The brain "frightens," perceives this as real death, and checks to see if the person is alive by sending impulses to the muscles.

20. Astral projection

A neuropsychological phenomenon in which a person, suspended between sleep and wakefulness, sees themselves from the outside. Mystics and occultists consider this a confirmation of the existence of the soul. The phenomenon is very difficult to study. While scientists know that the illusion of out-of-body experience does exist, they don't understand how it works or why it occurs. How to combat it is also unclear. Some people even deliberately enter this state to expand their cognitive capabilities.

 21. Sudden insight during sleep

Sometimes we can't find a solution to a problem for a long time, constantly thinking about it. And then, in our sleep, our brain itself suggests the answer; the main thing is to remember it. Everyone knows the example of Dmitri Mendeleev, who was struggling to create the periodic table and one day saw it in a dream. A similar story happened to the chemist Kekule—the formula for benzene appeared to him in a dream. Sometimes our subconscious already knows the answer, even though it hasn't yet reached our conscious awareness. And then, right in our sleep, insight strikes. What can I say, sometimes dreams offer such pleasant, unexpected bonuses.

The Strangest Things That Happen to Some People in Their Sleep

We're accustomed to thinking of sleep as a restful moment—a precious time when you can unwind from the hustle and bustle of the world and recharge your body, tired from the day. It's assumed we should wake up every morning feeling great and in good spirits. However, for some people, a night of sleep can turn into tragedy, crime, or even death...
During sleepwalking episodes, people are in a semi-conscious state—half of their brain is awake, the other half is asleep. They don't feel pain and are generally unable to evaluate their actions. However, they can still perform quite complex actions.
Here are 10 of the most unimaginable things people do in their sleep, from driving a car to jumping out of a window.

22. Sending email

Researchers at the University of Toledo report the case of a woman who woke up in the middle of the night, turned on her computer, and emailed party invitations to her friends. Although only one such case has been documented so far, the phenomenon already has a name: "Zzz-mailing." The woman fell asleep around 10 p.m. A couple of hours later, she wrote and sent three emails. One said, "Come over tomorrow and clean up this shithole. Dinner and drinks, 4 p.m. Bring only wine and caviar." Another briefly exclaimed, "What the...".
She had never experienced sleepwalking before and was understandably shocked the next morning when one of her friends called to say he'd accepted her invitation. Sleepwalkers often remember little or nothing of what they did in their sleep. Their consciousness is in an altered state, but they are capable of performing fairly complex actions. Researchers say the prescription medications the girl was taking may have caused her "Zzz-mailing.".

23. Jumping out of the window

People suffering from REM sleep disorder often act out their dreams. "Living like a dream" usually implies something positive, but not in their case. In 2007, a sleeping teenager fell out of a fourth-story window. After falling about 30 feet, he landed on the sidewalk, where he continued sleeping, unaware of what had happened. The teenager had not taken any alcohol or drugs.
Comedian Mike Birbiglia (pictured) once jumped out of a second-floor hotel window in his sleep and fell into the lobby. He woke up covered in cuts, requiring 33 stitches. Birbiglia, who has been diagnosed with REM sleepwalking disorder, admits to having suffered from sleepwalking for several years. "I remember often thinking, 'This could be dangerous. I should probably see a doctor...' And then I thought, 'Well, maybe I just need to get some dinner,'" the actor says.

24. Real "sleeping beauties"«

Victims of Kleine-Levin syndrome are often called "real-life sleeping beauties." They can literally sleep their entire lives away. Periods of drowsiness can last from a few days to up to eight months! During the rare moments of wakefulness, their behavior becomes unpredictable—they may cry without reason, binge eat, and even become childish. When they wake up after such periods, their bodies attempt to gradually return to normal, but it's not easy. They can go weeks or months without episodes of drowsiness, returning to normal cognitive function. Those with the syndrome undergo treatment, but its symptoms may never completely disappear.

25. Driving a car

Ambien (zolpidem) is a popular sleeping pill that frequently appears in driver arrests. Ambien users can exhibit bizarre behavior and always stand out from other drivers under the influence, especially if they exceed their dosage. They drive against traffic, crash into lampposts, and ignore police. In the past 10 years, there have been two reported cases of sleepwalkers driving into supermarkets. Another case involves a nurse, wearing only a thin nightgown in subzero temperatures, who crashed into another car and then decided to urinate in the middle of an intersection. When the police arrived, she began to fight them. Sleepwalking drivers often have a dazed look in their eyes. They rarely remember driving after taking the medication.

26. Ondina's Curse

Seventeen-year-old Liam Derbyshire (pictured) suffers from Ondina's Curse, a condition that affects 1 in 30 million people. Ondina's Curse is a disorder in which a person stops breathing as soon as they fall asleep. If they do, they can die within an hour. By 2006, only 200 cases were known worldwide. Patients require a tracheostomy—a tube inserted into the neck to aid breathing. To survive, they must spend their entire lives on a ventilator, which is connected to the tube when they go to sleep. Liam's parents must constantly monitor him to ensure he doesn't become tired and accidentally fall asleep, especially in the car. Ondina's Curse is so rare that many doctors never encounter it and may not diagnose it correctly in time.

27. Conquering heights

Seeing a silhouette on a tower crane at 2 a.m., passersby thought someone was trying to commit suicide. It turned out to be a sleepwalking girl who had apparently left her home unnoticed, slipped past construction site security, and managed to climb 40 meters in her sleep. The entire time, she had no idea she was within a hair's breadth of death. A firefighter climbed up to her but was unable to wake her, fearing that she would panic, fall, and die. The rescue operation ultimately took two hours—the girl was lowered down unharmed using a hydraulic lift. Her parents later admitted that she frequently suffered from sleepwalking.

28. Nightmares

True nightmares are not just "bad dreams," which are quite common and happen to almost everyone from time to time. Nightmares affect between 1 and 61% of children and less than 11% of adults. They occur during deep sleep phases, typically beginning in early childhood and fading by adolescence. Nightmare episodes can occur at intervals of several days or weeks, every night in a row, or recur repeatedly during the night.
The eyes of such parasomniacs are wide open, their faces express terror and panic, they sweat, and their heart rate accelerates. They often scream—at those around them or simply into the void—fighting, and seeming to be trying to escape from something. During these episodes, it's impossible to calm them down because they are, after all, asleep.

29. Murder

By 2005, 68 cases of "sleepwalking" murders had been recorded. For example, early in the morning of May 23, 1987, 23-year-old Canadian Kenneth Parks got out of bed, got behind the wheel in his sleep, drove more than 20 km, and broke into the home of his mother-in-law and father-in-law. There, he strangled his father-in-law until he lost consciousness and stabbed his mother-in-law with a kitchen knife, having first stabbed her with a tire iron. Most astonishingly, he then arrived at the police station, still in his sleep, covered in blood and panicked. The tendons in his hands were severed, but he showed no signs of pain. His electroencephalogram (EEG) readings, which are impossible to fake, were atypical, even for a sleepwalker. Ultimately, the court concluded that he had been sleepwalking throughout the incident and acquitted him.

30. Creating masterpieces of art

Lee Hadwin suffered from sleepwalking since childhood. It's no surprise, then, that he now leads a parallel life in his dreams. He began drawing in his sleep at the age of four, and as a teenager, his simple childhood drawings evolved into something more sophisticated. He's nicknamed "Kipasso." He says he feels strange because he has no interest in art or painting while awake. And he doesn't remember anything he did in his dreams.
When Lee isn't sleeping, he works as a nurse. He also played in a country band and claims to be much more interested in music than in painting. "I just can't explain where my painting comes from. It's as if a different part of my brain switches on when I'm asleep," says Hadwin. And, like other parasomniacs, he won't respond if you call him by name while he's painting.