Hypnagogic Jerk

After that post-Thanksgiving leftover indulging as many sneak to the couch for a bit of a nap, you might have a hypnagogic jerk. Most of us have had them but few know the proper name. It is an involuntary muscle spasm that occurs as a person is drifting off to sleep. The phenomenon is so named in reference to the hypnagogic state, or the transitional period between wakefulness and sleep. Hypnagogic jerks are also commonly known as hypnic jerks or sleep starts.

The muscle spasms may occur spontaneously or may be induced by sound, light or other external stimuli. Some people report hypnagogic jerks accompanied by hallucinations, dreams, the sensation of falling, or bright lights or loud noises coming from inside the head.

Sleep starts are quite common, with some research suggesting 60 to 70 percent of people experience them. Many individuals may be visited by nightly hypnic jerks without even knowing it, as the twitches often go unremembered, particularly if they don't cause a person to wake up.

Some scientists believe certain factors, such as stress, anxiety, fatigue, caffeine and sleep deprivation, may increase the frequency or severity of hypnagogic jerk. Researchers are also unsure exactly why hypnic jerks occur. One hypothesis is that hypnagogic jerks are a natural part of the body's transition from alertness to sleep, and occur when nerves "misfire" during the process.