Hypnic/Hypnagogic Jerks
What did you just call me?
I think we all know the feeling: there you are, sleeping peacefully or on your way to doing so, when out of nowhere, you’re abruptly jarred into consciousness. Sometimes it happens as part of a dream — maybe you’re falling, maybe you’re fighting. Some of us bank on it happening as part of a napping cheat code, whereas some of us just find it happening to us. But whatever the reason or circumstances, I think it’s safe to say we’ve all been there. But did you know that there’s a name for it?
Jay Summer and Dr. John DeBanto, of SleepFoundation.org, tell us that:
Hypnic jerks — also called sleep starts — are sudden, involuntary muscle contractions you may experience as you are falling asleep. Hypnic is short for hypnagogic, a word that describes the transition between wakefulness to sleep, which is when these jerks occur. Hypnic jerks happen seemingly at random as you are falling asleep, and typically only affect one side of the body, such as your left arm and left leg.1
Hypnagogic jerks tend to occur during stage 1 sleep. Doctors aren’t entirely sure why they occur: one theory is that nerves in the reticular brainstem periodically misfire, where your brain might mistakenly assume you’re falling (when you’re really just relaxing as part of falling asleep) and twitch your muscles so you awaken. They also might be a reaction to whatever dream accompanies them, and they may be exacerbated by excessive stress, anxiety, or caffeine consumption.
There doesn’t appear to be a specific way of preventing hypnic or hypnagogic jerks, other than exercising good sleep hygiene more generally. I kind of like “The Hypnic Jerks” as a band name — I wonder what kind of music they’d play…
Dr. Brandon Peters, of VeryWellHealth.com, differentiates a hypnagogic jerk, which happens as you’re beginning to fall asleep, from a hypnic jerk, which occurs upon awakening, which is consistent with my own research that the term “hypnagogic” relates to the moments just before falling asleep, whereas “hypnic” pertains to inducing sleep or sleep more generally.
Regardless of whether you differentiate the two, they’re both a type of myoclonus, or rapid, involuntary muscle movement, and tend to appear together with some mental imagery (e.g., fighting, falling, et al.).