You need to open the window
The very air you breathe could be an issue. “Close the door, shut the window, add a partner and a heater, and by 3am a typical bedroom sits at 1,500 to 2,500 parts per million of carbon dioxide,” says Dr Jemma King, author of Sleep First: Sleep Smarter, Think Sharper, Feel Better. “Research shows that above 1,000 ppm sleep efficiency drops, deep sleep reduces and salivary cortisol rises on waking. You’re sleeping, but your nervous system is mildly activated all night.” Luckily, it’s an easy fix: open a window – even 2cm will do the job, according to King.
