Twitching of the limbs and facial muscles while falling asleep, if not excessive, is a normal transitional wake-sleep phenomenon. Transitional states of sleep and wakefulness not uncommonly release brief and usually inconsequential motor and sensory phenomena, such as twitching, jerking (a prominent or nearly full body jerk is called a “sleep start” and is usually a normal variant), head or body rocking, tooth grinding (bruxism), making sounds, sleeptalking, hearing sounds/voices, loud bangs, or even explosions, or seeing things that are not there, which can be very unsettling. Also, brief moments of paralysis can take place during entry into sleep or arousal from sleep.

Any of the just-described events, when too frequent and/or intense, then becomes a clinical symptom that needs to be evaluated and perhaps treated. The brain is programmed to initiate state transitions and so with billions of neurons shifting gears during a change of state, it is not surprising that all sorts of little (or at times big) misfirings in the neurons are taking place, resulting in these motor and sensory events. It can take a little while for the brain to settle into its new state.

I recently wrote a book that considers this question while also describing the ever-growing set of abnormal behavioral and experiential phenomena emerging from sleep (the parasomnias) and their interactions with common sleep disorders. The book is called Sleep: The Mysteries, The Problems, and The Solutions (Penguin/Avery Press). Also, I produced and participated in a documentary film, along with eight of my patients, called Sleep Runners: The Stories Behind Everyday Parasomnias. 

—Carlos H. Schenck, Minnesota Regional Sleep Disorders Center, Department of Psychiatry, U of M Twin Cities campus