Decoding the phenomenon of people often startle when sleeping

According toLivescience, a hypnic jerk is a common phenomenon that occurs when people go through the transition between wakefulness and sleep. Hypnic jerks can occur spontaneously or be triggered by light, sound, and other external factors. Some people report being startled by hallucinations, dreams, the sensation of falling, or bright lights or loud noises in their heads.

Hypnoea jerks are common, occurring as the body begins to fall asleep, says Michelle Drerup, a sleep specialist at the Cleveland Clinic Sleep Disorders Center. Some studies suggest that 60 to 70 percent of people experience them. People typically don't remember having a hypnoea jerk unless they wake up from a nap.

Some scientists believe that factors including stress, anxiety, fatigue, caffeine intake, and sleep deprivation may increase the frequency and severity of hypnic jerks. However, there is not enough research to conclude this.

One theory is that hypnagogic jerks are a natural part of the body and occur when nerves gradually become "paralyzed" during the transition from wakefulness to sleep.

Another, more popular, evolutionary explanation is that the startle reflex is an ancient primate response to the muscle relaxation that occurs when the body begins to fall asleep. The brain misinterprets the relaxation as a sign that the primate is sleeping and has fallen out of a tree, causing the muscles to quickly respond.

"It's normal to startle yourself during sleep. However, if you startle yourself and it disrupts your sleep, you should see a sleep specialist to discuss your concerns," Drerup said.