What Causes Hypnagogic Jerks?

A hypnagogic jerk is the involuntary muscle spasm some individuals experience as they fall asleep. The name refers to the period between wakefulness and sleep: the hypnagogic state. Others may call the jerks 'sleep starts' or 'hypnic jerks.' Regardless, they're spontaneous or may occur from external stimuli. Patients may experience bright lights, loud noises, hallucinations, and the feeling of falling during a hypnagogic jerk. Currently, there isn't much conclusive research on causes. But some scientists believe they know certain contributing factors. For example, lack of sleep, consuming too much caffeine, and stress can all lead to hypnagogic jerks.