You close your bedroom door at night. The window is already shut because it’s getting colder outside, and that’s how you sleep for eight hours in a room with no fresh air.
The next morning you have a heavy head and a stale taste in your mouth, and you think you just didn’t get enough sleep.
There’s a chance you mostly inhaled your own exhaled air.
What happens in a closed room
With every exhale, you blow carbon dioxide into the room. During the day, that doesn’t build up because doors open and close and air keeps moving through your house. At night that doesn’t happen, and it accumulates in a space of a few dozen cubic meters, with the door closed and the window shut.
Outdoor air contains around four hundred CO2 particles per million. In a closed bedroom with two people in it, that can easily rise to two thousand over the course of the night, and sometimes even more. You don’t smell it and you don’t see it, because CO2 has no odor.
Why your body reacts to it
Your breathing is not regulated by oxygen. Your brain mainly looks at how much CO2 is in your blood, and that is the dial it uses to determine how deeply and how quickly you breathe.
If there is more CO2 in the air around you, you clear it less effectively and your breathing increases to compensate. You breathe a bit faster and more shallowly, and your heart rate rises a little too, while in a deep sleep phase the exact opposite is supposed to happen.
You rarely wake up because of it. What you’re left with is a night that gives you less, a heavy head that disappears after half an hour outside, and the feeling that your room is stuffy without it being warm.
The layer people miss
This rarely happens alone. The heating coming on and the windows staying closed also make the air dry, and dry air irritates your mucous membranes (causing them to swell and making your nasal passage narrower).
Then two things happen at once. Air that makes you breathe a little faster and a nose that lets less through than it did during the day. At that point, your body chooses the path of least resistance and your mouth opens, after which you spend the rest of the night breathing through your mouth.
That’s why a stale bedroom in autumn often ends with a dry mouth in the morning.
What you can do about it
Crack your window open. A centimeter is enough to exchange air all night, and it costs you almost nothing in heat, even in winter.
Can’t leave the window open because you live on a busy street? Then leave your bedroom door open. Your whole house becomes your air supply, and that’s plenty.
Air out the room for ten minutes with the window wide open before you go to sleep. That’s especially useful if the room has been closed all day, because then you start the night with a fully refreshed room.
Keep it cool. Around eighteen degrees works for most people, and fresh outdoor air helps you get there right away.
And make sure your nose can do the job. Fresh air is of little use if you can’t get it in, and your nose is never fully open on both sides anyway. Nasal strips pull your nostrils outward and keep your nasal passage open with a support strip. Mouth tape keeps your mouth closed so your body doesn’t switch over halfway through the night.
The habit for this week
Crack your window open before you get into bed. Every night, even when it’s cold outside and it feels illogical.
Keep an extra blanket handy if you get chilly. You sleep better cool and fresh than warm and stuffy :)
After a few days, notice your first ten minutes after waking up. That heavy, foggy feeling is the first thing to go.
1% Better Every Night.
Guy Veeke
PS: Do you wake up with a dry mouth even though your window was open?
Then it’s in the way you breathe. The combination of nasal strips and mouth tape keeps your nose open and your mouth closed, so the hours you put in actually pay off.
