Falling asleep is … well, it’s not the easiest thing in the world, otherwise we wouldn’t need all these tricks to help us do it. But it certainly seems like it should at least be one of the most relaxing activities that you can do. So why is it that sometimes, just as you’re on the cusp of drifting off and you feel yourself fading into dream time, your stomach suddenly drops and your body jerks you awake?
It’s really the worst part of the sleep routine (assuming you don’t experience sleep paralysis or night terrors). Why is it that at the very moment that you should be the most relaxed, you suddenly get seized with the feeling of falling through the air? It’s not uncommon. About 70 percent of people regularly face this experience, which is technically known as a hypnic jerk.
But what actually causes it? There are a few possible answers. One theory suggests that, as the muscles relax and the drowsy brain loses track of its surroundings, the occasional nerve will misfire, causing one of your extremities to twitch — that would account for some of the less unpleasant jerks. Another theory tries to explain the lurching, falling sensation with some ancient psychology. Perhaps in our tree-climbing primate days, the sensation of drifting off to sleep signaled the imminent danger of falling to the ground.
Another theory suggests that the jerk happens when the part of your brain that’s trying to fall asleep conflicts with the parts of your body that want to stay awake. Your muscles will relax as you drift closer to dreamland, but not all at once. Most of the time, sleepiness overtakes wakefulness easily, but sometimes wakefulness puts up a fight by overreacting and giving your muscles a sudden jerk. Read more