2 years ago
Last edited at 9:32PM on 11/9/2011
A hypnic jerk, hypnagogic jerk, sleep start, or night start, is an involuntary myoclonic twitch which occurs during hypnagogia, just as a person is beginning to fall asleep, often causing them to awaken suddenly. Physically, hypnic jerks resemble the "jump" experienced by a person when startled, often accompanied by a falling sensation. It usually happens with higher occurrence in people with irregular sleep schedules, sleep anxiety, fatigue, and discomfort.
According to the American Academy of Sleep Medicine there are a wide range of potential causes, including: anxiety, caffeine, stress, and strenuous activities in the evening. Close to 70 percent of all people experience this phenomenon just after nodding off.
Experts are still not completely sure why the body does this. The general consensus is that, as the muscles begin to slack and go into a restful state, the brain senses these relaxation signals and misinterprets them as indications of falling. The brain then sends signals to arm and leg muscles in an attempt to regain balance.
Scientists state that the sensation is completely normal for our bodies and is of little medical significance.