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.