Have you ever been on the cusp of sleep, only to be startled awake by a sudden, involuntary twitch of your arms or legs? This common phenomenon, experienced by an estimated 70 per cent of people in their lifetime, is known as a hypnic jerk or sleep start.
What Causes a Hypnic Jerk?
While the precise mechanism remains a mystery, sleep researchers have a leading theory. As we drift from wakefulness into sleep, our nervous system begins to wind down and our muscles relax. The brain can sometimes misinterpret this wave of relaxation as a sign that we are falling or tripping. In response, it sends a powerful, rapid signal to the body, resulting in the characteristic jerk.
These jerks are typically painless and often affect just one side of the body, though some individuals report a tingling or even painful sensation. For the vast majority, they are a normal, harmless part of the sleep transition and not linked to any underlying health issues.
When Should You Be Concerned?
In most cases, hypnic jerks are no cause for alarm. However, they can become problematic if they occur frequently over a long period, leading to anxiety about falling asleep and potentially contributing to insomnia.
Some research indicates a connection between frequent hypnic jerks and certain health conditions. A 2016 study suggested they could be a potential early symptom of Parkinson's disease. Experts stress, however, that it is highly unlikely for hypnic jerks to be the sole indicator; other more common symptoms like movement changes or REM sleep behaviour disorder would typically be present.
Medications can also play a role. Frequent hypnic jerks that disrupt sleep can be a side effect of some prescription drugs, particularly antidepressants like SSRIs (e.g., escitalopram, sertraline). Stimulants, including caffeine and non-prescribed substances like cocaine, have also been linked to these sleep starts. If you are on medication and experience concerning jerks, it is important to discuss this with your prescribing doctor.
Improving Sleep Hygiene to Reduce Jerks
While often unavoidable, certain lifestyle factors are believed to increase the likelihood of experiencing hypnic jerks. Managing these factors forms the cornerstone of good sleep hygiene, beneficial for everyone's rest.
Key triggers to be aware of include:
- Sleep deprivation
- High levels of stress and anxiety
- Excessive intake of stimulants like caffeine or nicotine
- Strenuous exercise close to bedtime
By addressing these areas—prioritising consistent sleep, managing stress, and moderating stimulant use—you can create a better environment for undisturbed sleep, whether you are prone to hypnic jerks or not.
The article was authored by sleep health experts Professor Yaqoot Fatima and Senior Lecturer Alexandra Metse from the University of the Sunshine Coast, and Lecturer Daniel Sullivan from Griffith University. It was originally published by The Conversation on Tuesday 30 December 2025.
