The scientific term for these “hypnic jerks” is a hypnagogic myoclonic twitch or flinch in your sleep. There is much debate about why they happen, but a generally approved theory is that as your body relaxes, your muscles slacken and your heart and breathing rate slow. Your brain misinterprets these signals and believes you are falling over. It fires signals giving you a knee-jerk reaction to extend your limbs and ready yourself to break the fall, which of course just results in your jerking your limbs, as you’re already stationary.
This is closely intertwined with waking up suddenly from dreams where you feel like you’re falling and you hit the floor, or by a vehicle, or if you’re drowning and you’ve run out of air. Your brain misinterprets the signals, thinking you are in grave danger, and releases a jet of adrenaline, initiating your fight or flight instinct. It’s often why you wake up suddenly after these dreams breathing heavily and practically crouching like a tiger.
It's not exactly known why hypnic jerks occur, but some theories suggest that they may be caused by changes in the electrical activity of the brain as it shifts from a wakeful state to a sleep state. Other possible causes include stress, fatigue, caffeine or nicotine use, and certain medical conditions such as anxiety or hyperthyroidism.
Scientists have said that hypnic jerks are more likely to occur in and are closely related to people who are suffering from sleep anxiety, fatigue, or simple discomfort. It is much more likely to happen to you if you’re actively fighting going to sleep, or haven’t had any sleep for over 24 hours. Having said that, there are many different stages of shutting down that your brain and body goes through in preparation for going to sleep, and for many, hypnic jerks is one of them. There is no damage to your mental or physical health short term .
For most people, hypnic jerks are not a cause for concern. They are not harmful and usually do not affect sleep quality. However, if you are experiencing frequent or severe hypnic jerks that are disrupting your sleep, or if you have other symptoms such as difficulty falling asleep or staying asleep, it may be a good idea to talk to your doctor or a sleep specialist. They can help determine the cause and recommend appropriate treatment if necessary.
