There’s a reason why you feel wide awake the instant you get in bed

There have probably been many times in your life when you’ve been exhausted as nighttime rolls around, and even though you’ve been dreaming about crawling under the covers, you just can’t fall asleep when you get into bed. As soon as your head hits the pillow you’re wide awake. It’s a cruel joke life plays on us sometimes, and sleep experts say there’s a reason it keeps happening to us.

Philip Gehrman, sleep-medicine specialist and assistant professor of psychiatry at the University of Pennsylvania, tells TIME this annoying phenomenon is called conditioned or learned arousal, and it usually arises because we’ve inadvertently taught our bodies that the bed isn’t meant for sleeping. For example, watching Netflix for hours under the covers or bringing your work into bed is sending the wrong message to your brain. Therefore, when it’s time to fall asleep you instead toss and turn and feel wide awake.

“If someone is a good sleeper, then each night they probably get in bed and fall asleep. So when they get into bed it triggers this auto response of sleepiness,” Gehrman says. That’s why he recommends no screen time in bed, as well as minimal reading — and only go to bed if you’re actually tired. You essentially have to retrain your brain to associate bed with sleep.

Of course, there might be some other factors in your life that are causing restlessness, such as a death in the family or a sudden change at work. Gehrman says this is called psychophysiological insomnia, and it can be treated with cognitive behavioral therapy for insomnia. Patients are able to change their sleep habits and schedule with this kind of treatment.

But if you don’t normally struggle with insomnia, sticking to the rules Gehrman laid out will likely help you fall asleep when you want to. Oh, and just in case you were wondering — yes, having sex in bed is totally allowed, and it shouldn’t disrupt your sleep schedule.