Hypnic jerks, also known as sleep starts, are those sudden, involuntary jolts you might feel as you’re drifting off to sleep, often making you feel like you’re falling. Though unsettling, they’re surprisingly common, affecting up to 70% of people.

The exact cause of hypnic jerks isn’t fully understood, but a few theories exist. One suggests that as your muscles relax when transitioning to sleep, the brain may misinterpret this relaxation as a sign that you’re physically falling, prompting a quick muscle contraction to “catch” your body. Another theory is that it happens due to the brain’s nervous system struggling to downshift smoothly into sleep, causing brief misfires and jerks.

Factors like stress, anxiety, or exhaustion can increase the frequency of hypnic jerks, as they keep the nervous system more alert. While generally harmless, they can disrupt sleep and cause frustration.

Understanding that they’re a normal part of the sleep process can help ease any anxiety they cause.