While experts don’t really know exactly why we need to sleep, they believe that sleep is necessary to allow our bodies and brains to recuperate.
So it’s natural to assume that once you close your eyes and fall asleep, nothing much will happen. Unfortunately, there are some really weird (and scary) things that can occur while you sleep. Here are seven:
1. You eat
A person with a condition called Nocturnal Sleep Related Eating Disorder will actually eat while they are asleep. According to Dr Tzvi Doron, clinical director at men’s health service Roman, “This is considered a parasomnia (sleep related disorder). They have no memory of eating when they wake up. One study estimated that almost 5% of the population has this disorder and it can be the cause of unexplained weight gain. Medication can be effective in treating this disorder, but it first has to be diagnosed correctly.”
2. You experience night terrors
The American Sleep Association explains that night terrors (or sleep terrors) are a parasomnia condition where you may react to a “foreboding sense of fear or terror by screaming, thrashing around or crying”. You may also get out of bed and walk or run around, and episodes can last as long as 20 minutes, after which you’ll get back to REM (or deep sleep) or wake up extremely confused.
The difference between a nightmare and a night terror is that you’ll experience a nightmare during the REM stage, while night terrors occur before the dream state of REM sleep.
3. You jerk uncontrollably
Just as you're falling asleep, you might have had the unnerving experience of falling and jerking away. This is called a hypnagogic jerk and is an involuntary muscle spasm that occurs as you drift off to sleep. It is named after the hypnagogic state, which is the transitional period between wakefulness and sleep.
Some experts believe that factors like stress, anxiety, fatigue, caffeine, sleep deprivation and intense physical exercise in the evening may increase the frequency or severity of these spasms.
"More often than not, hypnic jerks are completely normal and nothing to be concerned about," Michelle Drerup, a psychologist and behavioural sleep medicine specialist at the Cleveland Clinic's Sleep Disorders Center in Ohio, told Live Science. "However, if the jerks themselves, or the anxiety you experience about having them, are significantly disrupting your sleep, you should talk to a sleep specialist about your concerns."
4. You become paralysed
“I will wake up, but it’s only my brain which is awake. My whole body is locked in stillness. I can’t open my eyes, move my limbs or scream. It’s the worst nightmare you’ve ever had, only it’s really happening,” writes Jessica Barrett, who suffers from sleep paralysis.
According to Baland Jalal, a neuroscientist at the University of Cambridge and current fellow at Harvard University, the lack of scientific research into sleep paralysis possibly comes from a place of confusion – no one really knows what to make of it.
What we do know is that sleep paralysis occurs when a person falls asleep or wakes up. When it occurs, you’re aware of your surroundings but cannot move or speak. During a typical sleep cycle that lasts one to two hours, your brain goes through five stages – the first four make up non-rapid eye movement (NREM) sleep, while the fifth is when rapid eye movement (REM) occurs, which is when sleep paralysis can strike. During REM, which occurs about 90 minutes into a sleep cycle, your brain is most active, and produces the most vivid and emotionally-charged dreams.
“If you look at the pattern of neural activity in someone in REM sleep and compare that guy to a wakeful person, the brains of these two people look indistinguishable,” Jalal says. “Occasionally, the brain of the guy in REM looks more active than the guy who is awake.”
When we enter a state of REM, your body essentially paralyzes itself to prevent you from acting out any elaborate visions that could cause you (or your partner) harm. Under normal circumstances, you won’t notice but if you suffer from sleep paralysis, you are completely aware that you are unable to move.
During REM, our body regularly inhibits its motor neurons, paralyzing itself to prevent us from acting out REM’s elaborate visions and causing harm. Normally, the person is immersed in sleep and doesn’t notice they can’t move. Individuals with sleep paralysis, though, are completely aware of their immobility.
5. You groan
Have you ever woken up to hear your partner or child making the strangest noises in their sleep? They could have a condition called catathrenia (or nocturnal groaning), which the International Classification of Sleep Disorders (ICSD-3) classifies as a sleep-related breathing disorder like obstructive sleep apnoea or snoring.
It’s characterised as “groaning sounds emitted during expiration of breathing” according to the Alaska Sleep Clinic. These sounds usually occur during the REM stages of sleep and are often preceded by bradypnea breathing (or slow, long, deep breaths. A study published in the journal SLEEP found that all patients with cathathrenia had nearly identical symptoms of "deep inspiration without sound production followed by prolonged expiration with groaning, usually lasting from at least two to 20 seconds".
The difference between groaning and snoring is simple – groaning happens during expiration, while snoring happens during inhalation. Fortunately, this condition is not dangerous, other than disturbing your partner’s sleep.
6. You talk
Talking in your sleep is not an unusual thing – sometimes you might mumble incomprehensible sentences, other times you might express fully formed sentences.
“Sleep talking is actually a sleep disorder known as somniloquy,” says Dr Joyce Lee-Ionotti at Banner University Medical Center Phoenix. “Researchers don’t know a lot about sleep talking, like why it happens or what occurs in the brain when a person sleep talks. The sleep talker isn’t aware that they’re talking and won’t remember it the next day. If you’re a sleep talker, you may talk in full sentences, speak gibberish, or talk in a voice or language different from what you’d use while awake.”
7. You swear
Perhaps you don’t regularly drop the F-bomb in conversations – but that doesn’t mean you won’t swear in your sleep! A study conducted by Dr Isabelle Arnulf of the Pitié-Salpêtrière Hospital in Paris, France, revealed that in 10% of cases, sleep talking is rich in swear words and negative content. They discovered that swear words feature 800 times more during sleep discourse than during daytime talk.
Why? Dr Arnulf believes that this could be because when you talk in your sleep, it’s in response to a “negative dream situation that makes such impulsive and unguarded speech excusable”.
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