You are drifting off, then your whole body jerks like you stepped off a cliff. It has a name, and it is almost always harmless.
By Smartasaurus· 2 min read✨ Curious
You're warm, cozy, just about to drift off
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The short version
You are drifting off, then your whole body jerks like you stepped off a cliff. It has a name, and it is almost always harmless.
In a panic, your motor system fires a massive burst of electricity to your limbs.
The strange thing is that your brain is so committed to the mistake that it will often invent a dream to justify the twitch.
Your brain thinks you are falling to your death, so it tries to kick you back to life. It happens just as you start to drift off, when your body suddenly twitches with enough force to wake you up.
Scientists call this a hypnic jerk, and it is a side effect of two different systems in your head fighting for the steering wheel. One system wants you to stay awake and alert, while the other is trying to shut everything down for the night.
When the sleep system takes over, it starts a process called muscle atonia. This is when your brain sends a signal to paralyze your muscles so you don't act out your dreams and accidentally punch your headboard.
Sometimes, the transition happens too fast. If your muscles go limp before your brain is fully unconscious, your internal sensors get confused. They feel the sudden loss of muscle tension and misinterpret it as your body plummeting through the air.
In a panic, your motor system fires a massive burst of electricity to your limbs. It is a reflex intended to catch you before you hit the ground, even though the only thing you are hitting is your mattress.
Some researchers think this is a leftover tool from when our ancestors slept in trees. If a primate started to slip off a branch, that jolt would snap them awake in time to grab a limb instead of falling into the jaws of a predator on the forest floor.
You can actually make these jolts happen more often by drinking too much coffee or staying up until 3:00 a.m. When you're overtired, your brain tries to rush the process and skip the early stages of sleep, which makes that handover between being awake and being paralyzed much more violent.
While it feels like your heart is about to explode, the jerk itself is usually harmless. It is just a sign that your nervous system is a bit clumsy when it tries to turn itself off.
The strange thing is that your brain is so committed to the mistake that it will often invent a dream to justify the twitch. You might dream you tripped on a curb or stepped into a hole right at the exact millisecond your leg kicks, meaning your mind wrote a whole story in an instant just to explain why you're suddenly gasping for air.
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