There’s nothing more annoying than finally drifting off to sleep, only to be woken up mere moments later by your body jolting like you’ve stuck your finger in a plug-socket.
(Well actually, lying next to someone else whose involuntarily movement jerks you both awake is probably a bit more annoying.)
Anyway – why does this happen?
Dr Nas Fatih (@drnasneuro), a researcher in neuroscience and genetics at University College London, explained in an Instagram reel that “it could be because your brain is trying to save you”.
The phenomenon, known as hypnic jerks (or sleep starts), are “sudden involuntary muscle twitches that happen when your brain and body are getting their wires crossed during your transition to sleep,” he said.
You usually experience the jolting alongside an illusion of falling or a vivid dream – and it’s thought 60-70% of the general population experience them.
Why does this happen?
Dr Fatih said “we don’t fully know” but suggested it could be “a leftover from when our ancestors slept in trees or high places”.
“Your brain misinterprets relaxation during your sleep as falling from something, contracting your muscles ‘to catch yourself’ and prevent a fall,” he added.
Another fascinating theory is that the jerky movements are the body’s way of testing to see if sleep paralysis has kicked in.
As science writer Ada McVean explained in an article for McGill University: “During REM sleep the body is paralysed in order to prevent a dreamer from acting out their dreams.
“Some scientists believe hypnic jerks occur when the brain sends electrical signals to muscles to test for this paralysis, but it has not completely set in.”
According to Medical News Today, there are certain factors that increase the likeliness of you experiencing hypnic jerks, such as:
- extreme tiredness,
- stimulants (caffeine, nicotine, etc),
- stress and anxiety.
Or as Dr Fatih puts it: “Anything that keeps your brain in a heightened state of alertness can increase your chance of experiencing this jerk.”
Is it dangerous?
Hypnic jerks are very common and, for most people, are “pretty benign”, said the neuroscientist.
But if you find your sleep is dramatically impacted by them (ie. it’s causing insomnia), it’s important you speak to a doctor who may be able to prescribe medication to help.
The Sleep Charity suggests that if your jolting sensation is also accompanied by physical injury, bedwetting or confusion when awakening, it’s best to get checked out.