Have you ever been on the cusp of sleep, only to be startled awake by a sudden, involuntary jerk of your arms or legs? You're not alone. This common experience, known as a hypnic jerk or sleep start, is estimated to affect around 70 per cent of people at some point in their lives.
What Exactly Is a Hypnic Jerk?
The phenomenon often occurs during the transition from wakefulness to sleep. As the nervous system begins to wind down and muscles relax, the brain can sometimes misinterpret this state of deep relaxation. It mistakenly reads the signals as a sensation of falling or tripping. In response, the brain sends a powerful, rapid signal to the body, resulting in the sudden muscle twitch that jolts you awake.
Hypnic jerks typically affect just one side of the body and are usually painless, though some individuals report a tingling or even painful sensation. For the vast majority, these jerks are a normal, if occasionally annoying, part of the sleep process and are not linked to any underlying health issues.
When Should You Be Concerned?
While generally harmless, frequent hypnic jerks that disrupt sleep over a prolonged period can lead to anxiety about falling asleep and may contribute to insomnia. In some cases, they can be associated with other factors.
Research indicates that hypnic jerks may be more common in people with certain neurological conditions, such as Parkinson's disease. A 2016 study suggested they could be an early symptom. However, experts stress it is very unlikely for hypnic jerks to be the sole indicator; they would almost always occur alongside other, more reliable symptoms like changes in movement or REM sleep behaviour disorder.
Certain medications can also be a trigger. Antidepressants, particularly SSRIs like escitalopram, sertraline, and fluoxetine, list hypnic jerks as a rare but possible side effect. Stimulants, including medications containing caffeine and non-prescribed substances like cocaine, have also been linked to an increase in sleep starts. If you are on medication and experience disruptive jerks, it is important to discuss this with your prescribing doctor.
Lifestyle Factors and Sleep Hygiene
For most people, managing hypnic jerks is about promoting good overall sleep hygiene. Certain lifestyle factors are known to make them more likely to occur:
- Sleep deprivation
- High levels of stress and anxiety
- Excessive intake of stimulants like nicotine or caffeinated drinks
- Strenuous exercise close to bedtime
Controlling these factors is beneficial for sleep quality regardless of whether you experience hypnic jerks. Ensuring a regular sleep schedule, a calm pre-bed routine, and a comfortable sleep environment can help minimise their frequency.
The original article was authored by sleep researchers Yaqoot Fatima, a Professor of Sleep Health at the University of the Sunshine Coast, Alexandra Metse, a Senior Lecturer in Psychology, and Daniel Sullivan, a Lecturer in Clinical Psychology at Griffith University. It was first published by The Conversation on Tuesday 30 December 2025.
