The Science of Slumber: 5 Strange Things That Happen When You Sleep

 The science of sleep may seem pretty straightforward – it's the time we set aside for our bodies to recharge – but our brains actually stay quite busy while we slumber.

While you're spending around a third of your life sleeping, your brain is unconsciously processing complex stimuli, creating and organizing memories, and even flushing out toxic molecules. 

Then, there are the less common occurrences – the things our bodies do that we lose sleep over, or can even be cause for concern. While some of these events might feel other-worldly, their explanations are firmly rooted in science.

1. Sleep Paralysis

Have you ever had a moment where you wake up and suddenly realize you can't move, speak, or scream? You're not alone. About one in five people have experienced sleep paralysis, which can also be accompanied by visual, physical, or auditory hallucinations. During an episode, you might see a shadow in the corner of your room or feel someone's hands on your throat. 

Episodes can last from a few seconds to around 20 minutes, and the average length is between six and seven minutes. The whole ordeal sounds like a nightmare, but in reality, there's nothing to be scared of.

During REM sleep, our brains have vivid dreams. In order to ensure you don't physically act out the events of a dream, your brain temporarily paralyzes your entire body. This loss of muscle control is known as atonia. 

Sometimes though, the brain experiences a glitch and inadvertently wakes you up while your body is still experiencing paralysis. Waking up and not being able to move is scary on its own, but the dreams from REM can influence what you see or feel when you wake up, making the experience even scarier. 

2. Hypnic Jerk

Hypnic jerks, also known as sleep starts, are involuntary muscle movements that occur just as you're falling asleep. If you've ever been just about to slide into unconsciousness, but suddenly feel like you're falling and jump awake, that's a hypnic jerk. 

The muscle movements, called myoclonus, can be strong enough to wake a person, or gentle enough to not disturb the sleep at all. People may experience other symptoms alongside hypnic jerks, such as rapid heartbeat, rapid breathing, and sweating. 

There's no consensus on exactly what causes hypnic jerks, but they are related to the changeover between the sleep and wake cycles. As sleep paralysis sets in, the system that controls waking sometimes experiences a last burst of wakefulness before the system that controls sleep takes over completely. In other words, hypnic jerks are the last gasps of normal daytime motor control. Anxiety, caffeine, nicotine, stress, and sleep deprivation may make this more likely to occur. 

3. Sleepwalking

Sleepwalking — also known as somnambulism — involves getting up and walking around while in a state of sleep. It's more common in children, and usually occurs one to two hours after falling asleep during N3 sleep, the deepest stage of non-rapid eye movement (NREM) sleep. 

During sleepwalking episodes, sensory perceptions are virtually switched off, meaning the 'walker' does not fully perceive sights, smells, sounds, or even pain. 

Episodes typically last several minutes and can include walking around the house, completing a routine, driving a car, or even violence. Often, the person sleepwalking won't remember the episode the next morning. 

So, what should you do if you encounter a sleepwalker? Experts say simply guide them back to bed. If they won't follow, simply observe them to ensure they're not doing anything to hurt themselves or others. 

4. Lucid Dreaming

During a lucid dream, a person is completely aware that they dreaming. The dreamer can use this awareness to gain control of the dream, the characters, environment, and the narrative. 

Around 55 percent of people naturally experience a lucid dream once or more in their lifetime. Others work to train themselves to dream lucidly. Aside from the fact that it could simply just be fun to control your dreams, lucid dreaming also has practical applications, such as being used to combat nightmares. 

Dr. Denholm Aspy, at the University of Adelaide in Australia, is a researcher who specializes in lucid dreaming. He explained to MNT:

“Let’s say you’re being attacked by someone in a nightmare. You could try to talk to the attacker. You could ask them, ‘Why are you appearing in my dreams?’ or ‘What do you need to resolve this conflict with me?'”

5. False Awakening

Imagine you're having a bad dream. You finally wake up, and the monsters are gone. After catching your breath, you walk to the bathroom to splash some cold water on your face. You look up into the mirror and scream – you were wrong. The monster is right behind you. You thought you were awake, but really, you're still dreaming.

A false awakening is a phenomenon that can happen to anyone. Sometimes it can be a dream within a dream, or maybe a dream within a dream within a dream, like a Russian nesting doll.

Similar to lucid dreaming and sleep paralysis, false awakenings are considered one of the hybrid states between sleep and wakefulness. It can be caused by sleep apnea, insomnia, anxiety, or mixed brain states.