You are finally comfortable, your eyes are closing, and sleep is almost there. Suddenly, your leg jerks, your foot kicks, or your whole body gives a quick jump. For a moment, you are wide awake again, wondering what just happened. This strange experience is more common than you might think. These sudden movements are often called hypnic jerks or sleep starts. They usually last only a moment, but the reason they happen is more interesting than you might expect.
