Why Humans Suddenly Jerk Awake While Falling Asleep, According To Science

Ever start to drift into a peaceful sleep and suddenly become overwhelmed by a sense of falling, then find yourself jerking awake? Or, have you received complaints from a partner about kicking them as you drift off? This is actually a very common phenomenon known as a hypnic jerk, also referred to as a hypnagogic jerk. In fact, approximately 70% of people experience this at some point in their lives, with around 10% of that statistic experiencing hypnic jerks on a nightly basis.

While the exact neurological mechanism underlying this is unknown, there are some compelling hypotheses. Many suggest that these jerks are the result of unstable activity in the reticular formation of the brainstem while transitioning from wake to sleep. The brainstem regulates involuntary bodily functions and reflexes, and the reticular formation is an important modulator of wakefulness and wake-to-sleep transitions. Essentially, as the nervous system transitions to inhibit motor commands for sleep, some evidence suggests that altered signaling from the reticular formation could induce sudden muscle contractions.

Additional theories state that this is a leftover evolutionary function from non-human primates who would regularly sleep in trees. This hinges on the idea that the body interprets the muscle relaxation that accompanies sleep as falling. Still, others assert that this could be a result of a hyperactive sympathetic nervous system, typically resulting from stress and anxiety.

As alluded to above, anxiety and stress are risk factors for hypnic jerks. Partially, this could be due to the aforementioned theory that anxiety induces an overactive nervous system. However, a common symptom of stress and anxiety is insomnia. This could exacerbate this phenomenon as sleep deprivation also increases the risk of hypnic jerks. Recent studies have additionally suggested that selective serotonin reuptake inhibitors, which are commonly prescribed to treat anxiety disorders, are associated with hypnic jerks.

Another often-noted risk factor is the use of caffeine prior to sleep. While there is perhaps a biochemical mechanism associated with caffeine underlying this, one should note that caffeine prior to sleep can also contribute to sleep deprivation, which has already been mentioned as a risk factor. Whether stimulants present an independent association with this phenomenon or downstream effects of stimulants, such as poor sleep, are the more likely culprits requires further research.

Interestingly, while exercise is broadly considered to improve sleep, working out shortly before bed or exercising more than eight hours per week can increase the risk of hypnic jerks. Timing physical activity earlier in the day and making sure to rest between strenuous workouts could potentially mitigate these effects. Therefore, moderation appears to be the key in maximizing the beneficial effects of exercise on sleep.

Generally speaking, hypnic jerks are harmless and the worst one can expect is to pull a muscle, although even this is rare. However, sometimes these strange movements are indicative of a more harmful underlying health concern, usually when they accompany additional symptoms throughout the day. In particular, hypnic jerks have been observed in connection with Parkinson's disease. This is a neurodegenerative disorder in which there is a significant loss of dopamine-producing cells in a part of the midbrain important for movement.

Parkinson's disease symptoms normally include tremors, impaired movement, alterations in speech, and muscle rigidity. Recent studies have found that hypnic jerks are commonly seen early on in the disease. Therefore, although hypnic jerks are incredibly normal, if you notice them occurring with additional movement difficulties while awake, contact a healthcare provider to discuss any concerns.

Some steps may be taken to avoid these pesky movements in general. First and foremost, attempt to get the right amount of sleep and have a consistent bedtime routine. This helps let your brain know that you are winding down. Second, exercise strategically and avoid late-night trips to the gym. Third, consume caffeine in moderation, aiming for 400 milligrams or less per day. And, similar to exercise, try to restrict caffeine intake to a time well before you plan to sleep. Finally, if the option is available, reduce stress through participating in relaxing activities.