Many conditions can cause large jerks of the body, known as hypnic jerks, including nightmares, intense stress and previous exercise, writes the American Academy of Sleep Medicine. Hypnic jerks occur in up to 70 percent of normal individuals as part of the process of falling asleep, but repeated hypnic jerks may disrupt sleep to the point where sleep deprivation becomes problematic. Repeated hypnic jerks may also indicate a more severe, underlying medical condition.
Hypnic jerks most often occur in healthy individuals shortly after falling asleep, according to the AASM, and are often accompanied by a falling feeling or a sensory flash. These jerks may not always wake sleepers who experience them, but a sufficiently strong jerk or several in a short span of time is often enough to disrupt sleep. People experiencing hypnic jerks may also injure themselves or others from the motion.
Sleep scientists consider distressingly intense or common jerks during sleep a form of pathological myoclonus, according to Mayo Clinic. Some cases of intense jerking while asleep have no obvious cause and are classified as essential or idiopathic myoclonus. However, a wide variety of neurological conditions can cause these types of jerks, as can some non-neurological diseases, such as liver or kidney failure and some rare genetic disorders. Excessive caffeine intake or abuse of drugs may also result in hypnic jerks. Finally, hypnic jerks are often observed as a symptom of sleep apnea, writes WebMD.