Why you jerk awake just as you’re about to fall asleep

You’re in bed. It’s been a long day and the lights are off. Everything is quiet and peaceful. You can feel yourself dozing off. Right before you do, you feel like you’re falling in the air and all of a sudden you jolt awake. You’ve invested all this time into finally getting comfortable and sleepy and your body has rudely decided to interrupt what could have been the start of a good night’s sleep. Not sure what I’m talking about? Watch this cat.

What is it?

This phenomenon is known as hypnic jerks (or sleep starts/sleep twitches). Hypnic jerks are involuntary body twitches, muscular jolts or movements that occur when your body transitions from being awake to being asleep.

Why does it happen?

Scientists still aren’t sure why hypnic jerks happen. There are several main theories that try to explain why they occur.

“Abort sleep” mechanism

Sleep experts suggest that it might be a way for your brain to decide if wants to go to sleep or stay awake. You could see it as a neurological battle between the system of your brain that wants to keep you awake and alert against the system in your brain that encourages you to sleep. “Battle of the brain”. Image by author. According to Dr Carl Bazil, Professor of Neurology at Columbia University, “one of the things that happen as you fall asleep is your muscles relax, but the awake part [of your brain] may still be stimulating enough that it will temporarily overreact and you get this jerk of muscle activity”. Evolutionary reflex “Falling out of the tree reflex”. Image by author. Several evolutionary theories suggest that hypnic jerks are an built-in response hardwired into our brain to increase our chances for survival. One theory suggests that these jerks prevented your primate ancestors from falling out of a tree. Another theory suggests that these jerks wake you up so you can double check there are no predators nearby that could gobble you up. Read more about these theories here. Limbs preparing for REM “Brain deactivates limbs in preparation for REM”. Image by author. Another theory is that your brain shuts down as you prepare to go to sleep, and deactivates limb control in preparation for REM (rapid-eye movement) activity. Sleep paralysis occurs during REM, which is why you don’t act out your dreams when you’re asleep. So, hypnic jerks might be one of the side-effects of your brain preparing to deactivate your limbs. Nerve misfiring “Nerve misfiring”. Image by author. One idea suggests that when we go from consciousness to sleep, our nerves might misfire, causing hypnic jerks right before we fall asleep. You could think of it as a plane taking off: when travelling from being awake to being asleep, you might experience some turbulence (or in this case hypnic jerks from nerves misfiring) before you’re safely up in the air and on your way to a good night’s sleep.

Things that make it worse

The good news is hypnic jerks are completely harmless, so there’s no need to panic. The bad news is that there isn’t anything you can do to stop them. However, these are things that can make hypnic jerks worse are:

Caffeine – consuming lots of caffeine can cause more frequent jerks, so you might want to rethink that third cup of coffee. Anxiety and stress – people suffering from short or long-term stress can be more prone to hypnic jerks. Anxiety disorders can also cause sleep problems and abnormalities, which can lead to increased hypnic jerks. Sleep deprivation – if you’re sleep deprived, you might experience more sleep-related problems. Extensive sleep deprivation can increase your chances of having hypnic jerks.

Want to learn more about these factors? Have a look here. Suffer from a bad case of hypnic jerks or another sleep disorder? Visit here for help.