Illustration: Kieran Blakey

The Nuance

This Is Why You Keep Waking Up In the Middle of the Night

The science behind that silent, malfunctioning alarm clock in your brain

Published in
5 min readJan 9, 2020


It’s three a.m., but you don’t need to check your phone to know that.

You know it’s that time because you always wake up at three a.m. It’s like your brain is equipped with a silent, malfunctioning alarm clock that rings you awake each night despite your earnest intention to sleep soundly for a full eight hours.

The funny thing is that everyone wakes up multiple times each night. But in most cases, these middle-of-the-night arousals are so brief and shallow that the brain doesn’t recall them in the morning.

“The average adult awakens seven to 15 times each night, and this is normal,” says Michael Perlis, director of the Behavioral Sleep Medicine Program at the University of Pennsylvania’s Perelman School of Medicine. He says these arousals tend to be “amnestic,” meaning a person doesn’t usually remember them. They last anywhere from a few seconds to a few minutes, and they usually coincide with transitions from one sleep stage to another. “Exactly why these happen is up for debate,” Perlis says. “But you tend to shift your body position when you have these brief awakenings, and that’s a good thing.” If your sleeping body were completely motionless all night long, this prolonged period of stasis could lead to skin sores, loss of muscle tone, or other issues that arise in people who are bedridden and unable to move due to illness or infirmity, he says.

But for some people, one or more of these middle-of-the-night arousals are neither short nor amnestic. And there are several common explanations for these predictable awakenings.

Perlis says sleep-related anxiety is one possibility. If someone is anxious about getting a good night’s sleep, their brain may be on high alert for periods of wakefulness. When one of those shallow, run-of-the-mill awakenings happens following the night’s first cycle of deep sleep, an anxious brain may take notice with an “oh, shoot” emotional reaction. Perlis says this may cause a person to wake up more fully and for a longer period of time than is typical. And because sleep stages tend to happen at regular…



Markham Heid

I’m a frequent contributor at TIME, the New York Times, and other media orgs. I write mostly about health and science. I like long walks and the Grateful Dead.