Some things that we can't do in our sleep are obvious, like cook a meal or run a marathon (unless you can, and then we, and many sleep researchers, would like to hear from you).

Other things that sleep prevents aren't so obvious. If you can walk in your sleep, talk in your sleep, and in some cases scream in your sleep, and still not wake up, then coughing isn't a big deal, right?

Wrong.

Here are three unexpected things you can't do while sleeping:

You can't sneeze while asleep

Sleep researcher Steven Shea, director of the Oregon Institute of Occupational Health Sciences at Oregon Health and Science University, told Popular Science he's worked on hundreds of sleep studies, and no one has ever sneezed while asleep. He has a theory as to why, involving non-REM and REM stages of sleep. During non-REM sleep, or deep slumber, stimulus that would normally make you sneeze, like tickling a feather under your nose, simply can't get through. If the stimulus is strong enough, like a loud noise, the smell of smoke, or maybe a serious feather tickle, you simply wake up and then sneeze. During REM sleep, however, the stage where your eyes flicker behind your lids and you dream vividly, your muscles are actually semi-paralyzed to prevent acting out dreams, which also prevent the big achoo.

You can't cough while sleeping

Seems coughing, just like sneezing, is not possible while sleeping. In one sleep study, Shea studied a boy with a chronic cough. Though the child coughed persistently every 10 to 15 seconds while awake, his cough subsided during sleep, for the same reason you cannot sneeze while sleeping. When people are sick and feel like they've been up all night coughing, that's because they haven't really slept. Every time you cough during the night, you actually wake up for milliseconds, cough, then return to sleep.

You probably can't yawn in your sleep

Sleep researchers are still studying this one, but most theories believe yawning is either an empathic reaction to others — you yawn when your BFF does — or a means of temperature regulation that cools the brain by shunting blood to facial muscles, according to a study in the journal Sleep Breath. Regardless of why you yawn, which is still up for debate, Matthew Ebben, the director of lab operations at New York Presbyterian Hospital/Weill Cornell Medical Center, told The New York Times there have been cases of people yawning in their sleep, but it's rare. Since you mostly yawn when tired, bored, before sleep or upon waking, it's not likely most of us do it during sleep.

Now if only you could really clean the house while asleep.

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