Hypnic jerk or Sleep start
You’re lying comfortably in bed, your heavy eyelids starting to close, when suddenly, you jerk awake, muscles tensed and gasping for air, because you feel like you just fell off a cliff. Then you look around and realize you’re safe at home before sinking back onto your pillow, where you either nod off without incident or lie awake all night, wondering: What was that?
There’s a name for this phenomenon: It’s called a hypnic jerk or sleep start. It’s a sudden increase in muscle activity that happens to just about everybody and can be quite literally startling, though the intensity depends on the person, says Carl Bazil, M.D. Ph.D., director of the Sleep Disorders Center at New York–Presbyterian/Columbia University Medical Center.
Some people just twitch and don’t wake up (…) Others actually cry out in fear (…)