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Having trouble sleeping? In this episode of SciShow, Hank explores different kinds of sleep disorders, from insomnia to apnea to sleepwalking.
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Say you've been napping like between classes or after a long night out or, I don't know, after broadcasting on YouTube for 48 straight hours to raise money for charity.  Now imagine you're awaking up and suddenly you discovered that you can't move.  You wanna speak but you can't, your mind is acutely aware of what's happening but you're powerless to get your body to do anything.  It may last a few seconds, it may last a few minutes, in rare cases it can last more than an hour.

It's called sleep paralysis and you might not have to imagine it because up to 40% of us have experienced this sleep disorder in some point in our lives. I am one of them.

We don't like to think about the bad things that can go on while we're in dreamland just as we hate the disorders that keep us from even falling asleep.  Hello insomnia.  But even though we've talked a lot on this show about the signs of sleep (why we need it, why we dream, and where dreams come from), there is a whole other polymorphously messed up realm of human biology that explains what happens when sleep turns against us.

We can't turn our brains off, we forget to breathe, we have waking hallucinations, some of us even walk, eat, run, and have entire conversations when we're asleep. The half-asleep brain is a crazy place and once you understand it you may never see the back of your eyelids the same way again.


When most people think of the things that cramp our sleep style, they think insomnia.  But defining, diagnosing, and treating this most common sleep disorder can be tricky.  In fact, for a long time, most scientists considered insomnia to be a symptom of another problem like depression, anxiety, asthma, stress, substance abuse, a traumatic injury, even jet lag. Though, today, insomnia is considered by many to be a chronic disease of its own that interacts with other medical conditions.

So if you've ever had prolonged trouble falling asleep or staying asleep, but you don't have any other health issues, then doctors would probably say that you have primary insomnia. If you do have something else going on, like a physical or psychological condition, then you've got secondary insomnia. And most cases of secondary insomnia are chronic, meaning it lasts for more than a month.

There are also cases of acute, or short term, insomnia which is usually triggered by stress or some specific life event. Whatever the cause, scientists believe these insomnias are the result of the simple but eternal struggle between arousal and sleepiness.

More and more research is suggesting that a condition known as hyper-arousal, where the nervous system remains in a constant state of alert, may be the main reason for chronic insomnia. Hyper-arousal is basically a prolonged version of your body's fight-or-flight response. You know that feeling, your stress hormones are amping up, your heart and respiration rates increase. For most people this response disappears pretty quickly, but for many insomniacs it can last all day into the night and that makes it difficult for the body to relax, obviously.

But what's there to be afraid of once you have dozed off?  Well sleep apnea is one of the more serious disorders.  Simply put, it's when your breathing is interrupted while you're sleeping. Apnea comes from the Greek word for "want of breath." For some people, it happens once or twice per night. In serious cases it can happen more than a hundred times per hour. Though relatively common, more than 12 million Americans have it, the most severe forms of sleep apnea can lead to heart failure and stroke. It's also been linked to diabetes.

One of the more troubling aspects of sleep apnea is that the victims don't always realize they have it. The most common form, obstructive sleep apnea, happens when the muscles at the base of the tongue and the uvula, that fleshy piece of tissue at the back of the throat, collapse.  If this collapse blocks the airway only partially, then you get snoring as air tries to squeeze through. But apnea occurs when the airway is completely blocked.

When this happens, block oxygen levels drop fast, which in turn tells the brain that breathing has stopped and that those muscles have to reopen the airway post haste. But this whole conversation between your body parts can last from a few seconds to a few minutes, usually without the person ever waking up. Needless to say, though, this does not make for very restful sleep.

There are all kinds of treatments for this kind of apnea, but most people end up using a continuous positive airway pressure, or CPAP, machine. It has a mask that fits over the mouth and nose and gently blows air into the throat, helping to keep the airway open which doesn't sound very restful either.

Another type of disorder, central sleep apnea, is much more rare. Instead of a physical blockage in your throat that prevents breathing, this is an interruption of the brain signals that tell the body to breathe. Until recently there were few effective treatments but scientists are experimenting with a new pacemaker-like device that sends an electrical impulse to stimulate the diaphragm to breathe during sleep.

Okay so forgetting to breathe is pretty bad but sleep disorders get downright dangerous when it comes to sleepwalking. Partly, though, because it affects about 15% of people.  It is more common in children between the ages of 3 and 7.

Sleepwalking, also known as somnambulism, almost always occurs during the first third of the night. That's the part of the sleep cycle we call non-rapid eye movement sleep and it's generally a period of deep sleep characterized by slow brain waves.

While there's no consensus as to what causes this condition, there are a few theories as to why people begin walking, eating, running, even having conversations while the brain thinks it's asleep.

Some scientists think it's caused by the brain trying to circumvent other stages of sleep and go directly from deep, non-REM sleep to full-on wakefulness. Others point to a chemical messenger in our bodies known as GABA which normally serves to slow down activity in the brain's motor system. Turns out that children lack the fully developed neurons that release GABA so without a full network of connections in the brain to keep motor activity under control, it may be easier for young brains to instruct the body to move around while it's asleep. Which is crazy because have you seen how much children move around when they're awake?!

Sometimes the causes of sleepwalking are external and pretty controllable, like sleep deprivation, stress, and drug use. But scientists have also discovered that some people are genetically predisposed to it. A study conducted on families with at least four generations of sleepwalkers have traced the condition to a defective section on chromosome 20. And a mother or father who carries this defect has a 50% chance of passing it on to their children.

But this is not the case with sleep paralysis which I experience sometimes. It's a little weird, sometimes even a little scary, though I know it's temporary. But why does this happen? Why does my brain and my body decide to freak me out first thing in the morning?

In some cases, sleep paralysis is a symptom of narcolepsy, a disorder that causes people to have an overwhelming need to sleep. But it also regularly happens to non-narcoleptics, like me.

The weird feeling of being conscious but unable to move generally occurs as you're falling asleep but it can also strike you as you're waking up. Scientists believe that a main cause is entering REM sleep soon after lying down, bypassing the stages of non-REM sleep that normally happen first. Typically, REM dominates the later stages of sleep, which are also when the most vivid dreams occur. During this deep sleep your muscles are essentially paralyzed, most likely to prevent you from acting out whatever crazy space unicorn riding dream you're experiencing.

Sleep paralysis occurs when you wake up in the middle of all of this and suddenly you're aware of the fact that moving is impossible. Recent studies have also found that the same neurotransmitters that affect sleepwalking may also cause sleep paralysis.

University of Toronto's scientists discovered that both GABA and glycine switched off the brain cells that allow muscles to be active during REM sleep, at least in lab rats. Now in the most severe cases of sleep paralysis, victims also experience frightening and bizarre hallucinations. They can be visual or auditory and often involve shadows or hearing voices and footsteps or seeing images of humans and animal figures. Occasionally victims will also feel pressure on their chest and have trouble breathing. Scientists have described this phenomenon as dreaming while awake.

Me, I prefer to do my dreaming while sleeping, thank you very much. And hopefully I didn't make you afraid to go to bed tonight.

Thank you for watching this SciShow Infusion, especially to our Subbable subscribers whose contributions make SciShow possible. This episode comes to you from our latest president of space, Doug Mestanza, who wants to wish a happy birthday to Sasha Korzenska. To find out how you can be president of space go to and if you have any questions or comments or ideas for us you can reach us on Facebook or Twitter and don't forget to go to and subscribe.