Let’s say you’re having a busy day and things are taking a little longer than planned. Suddenly it’s lunchtime and your to-do list is only half done. You try to cross everything off and somehow still manage to get to bed at a decent hour. Success! But then, lying in the dark, you can’t sleep, even if you’re completely exhausted.

Sound familiar? Harris says this is a prime example of the brain fatigue that occurs when we don’t give our minds enough time to relax and recover before bed. “When you’re going, going, going, it’s hard to turn off your brain,” she tells mbg, making it hard to fall asleep and/or stay up through the night.