You’re all cozy, covered in your fave blankets and feeling all warm under the covers. You close your eyes and start to doze off. . . only to jerk awake, your muscles tensed, your stomach lurching like you just missed the last step on a flight of stairs. It’s happened to us all, but why?
There’s actually a name for this, as The Cut reports: it’s called a “hypnic jerk” or “sleep start,” and it can happen to anyone. In fact, according to Live Science, up 70 percent of people experience these jerks right before they’re falling into a blissful sleep.
The sudden increase in muscle activity can be intensely frightening, though it all depends on the person. “One of the things that happens as you fall asleep is your muscles relax, but the awake part may still be stimulating enough that it will temporarily overreact and you get this jerk of muscle activity,” Carl Bazil, M.D. Ph.D., director of the Sleep Disorders Center at New York–Presbyterian/Columbia University Medical Center, told The Cut.
Some people twitch in their sleep, but it’s not intense enough to wake them up. Others, however, have such vivid sleep starts that they actually cry out when they wake up — often because it was accompanied by a bad dream or visual component of some kind (like falling of a cliff, for example). In an essay for BBC, psychologist Tom Stafford, coins this “dream incorporation,” in which “something external, such as an alarm clock, is built into your dreams.”
“When this does happen, it illustrates our mind’s amazing capacity to generate plausible stories,” he writes. So yay for us!
However, according to Dr. Bazil, it seems to be a sort of fight between different systems in your brain — one that keeps you awake and one that helps you fall asleep. But because it’s not a phenomenon that is considered harmful, there isn’t much research on the topic.
While not harmful, sleep starts can be seriously annoying, and there are things that can trigger them. Sleep starts can be worsened by, ironically, not getting a good night’s sleep (talk about a catch-22), so making rest a priority can ease them. Tobacco and stimulating medication can also worsen it, but the absolute worst culprit? “The most common culprit by far would be caffeine,” Dr. Bazil told The Cut. “If it’s bothersome, the first thing I tell people is to cut back on the caffeine, especially late in the day.”
Another form of this is your head bobbing when you fall asleep sitting up (in class, in a meeting. . . hopefully not during a particularly boring conversation) that leads to sudden muscle jerks. This is thought to be an evolutionary adaptation for when our ancestors were in trees. Obviously, if they fell asleep in the wrong position, they could plummet to their death — and that “WAKE UP” trigger still happens now.
So the sleep jerks in bed — you can chalk that up to your brain being annoying. But waking up during a meeting? Your body’s just got your back.
(Image via Fox.)