Just after falling asleep, you may awaken with a sudden jerking movement, often referred to as “sleep starts.” The technical name is “hypnagogic jerk,” which is a sudden and strong involuntary twitch or muscle contraction that occurs while an individual is beginning to fall asleep. It may affect only part of the body — like an arm or leg — but more commonly seems to cause the entire body to jolt suddenly. These movements may occur without waking the affected person. If an awakening does occur, these sudden movements are often associated with a brief mental image. For example, you might believe that you were falling. A leg movement may incite a fragmentary dream image that you were perhaps kicking a soccer ball. Sleep starts can be a normal part of sleep. In fact, it's estimated that 60%-70% of people recall experiencing them. If they occur infrequently, as they often do, they're not normally distressing. However, frequent events may lead to anxiety about falling asleep, resulting in insomnia. Hypnagogic jerks typically occur during Stage 1 sleep, which is the lightest stage of sleep that occurs right after falling asleep. Sleep starts occur more often with the increased use of caffeine and other stimulants and can be provoked by physical exercise or emotional stress. While they can be startling, hypnagogic jerks are completely normal, extremely common, and are rarely a sign of any underlying condition.
