You’ve probably felt it. As you drift into peaceful slumber, you’re suddenly jolted awake by the overwhelming feeling of falling backwards into the void. You may gasp for air and your limbs or whole body may spasm. During an experience like this, it’s not the falling sensation itself that thrusts you into consciousness – it’s actually the strength of the muscle contraction (a weak one might not even wake you), which is called a hypnic jerk.
What is a hypnic jerk?
This benign experience is called a hypnic jerk (also referred to as hypnagogic jerk or sleep start) and it’s much more common than you might think. Hypnic jerks are a type of involuntary muscle spasm called myoclonus (hiccups fall under this umbrella, too). Seventy percent of people experience a hypnic jerk at least once in their lifetime.
Why do they happen?
Scientists don’t know exactly why we experience hypnic jerks as we drift to sleep, but there are many theories surrounding their purpose. The first is the theory of evolutionary reflex. Once upon a time, the primates from whom we evolved slept in trees to protect themselves from predators. As their muscles relaxed, their brains initiated involuntary muscle spasms to keep the primates awake and alert them to the risk of falling from a tree to their imminent death. According to this theory, other potential uses of the hypnic jerk as an evolutionary reflex include:
- Psychological priming: A reminder to complete all tasks necessary for survival before hitting the sheets like consuming an adequate amount of food and securing shelter
- Predator scan: A reminder to make one final scan for predators in the vicinity before falling asleep
Another potential explanation for hypnic jerks is nerve misfiring, which is exactly as it sounds. Some believe that as we drift to sleep and our bodies bounce between wakefulness and rest, our nerves inherently misfire, causing our muscles to contract as we fall asleep. This theory does not address why 30% of people never experience a hypnic jerk or why they don’t occur daily in those who do experience the sensation.
Hypnic jerks may be an indication that your limbs are preparing to enter REM sleep. During REM sleep, your muscles relax through a process called REM muscle atonia to prevent you from physically acting out your dreams. Due to abnormal brain activity during this transition, hypnic jerks may occur.
There are many more theories as to why hypnic jerks occur.
Can you prevent hypnic jerks?
Very little research is devoted to the study of hypnic jerks because they are harmless, but scientists have discovered a connection between the occurrence of hypnic jerks and night sweats, rapid breathing and rapid heart rate. This means hypnic jerks may be triggered by stress, stimulants (like coffee or nicotine), sleep deprivation and high levels of activity before bed. If hypnic jerks keep you awake at night, try new techniques for managing stress like meditation or breathing exercises, exercise in the morning and skip the afternoon coffee.
If you’re one of the billions of people who experience hypnic jerks, there’s no need to worry. Hypnic jerks are completely harmless, so the next time you feel like you’re falling into the void, laugh it off, take a few deep breaths and start counting sheep. You’ll be asleep in no time.