Why does my body jerk when I’m falling asleep?

Dear Cecil: Sometimes when I am sleeping I will jerk and wake myself up. My friends say that I am dreaming about falling, and that if I hadn’t jerked and woke myself up I would have died. Is this true? I mean, the only thing I could fall off of when I am sleeping is my bed. But I don’t believe I could die. Uncle Cecil, is this an old wise tail? Sandy K., Phoenix

Cecil replies:

An “old wise tail,” whatever that is, no. An old wives’ tale, quite likely. However, there’s a slim chance you have a serious problem, so listen up.

Many people, when they’re drifting off to sleep, experience something called “hypnagogic myoclonus,” which we’ve discussed in this column in the past. This basically consists of sudden full-body twitches, and often it’s preceded by a sensation of falling. It’s not clear why myoclonus occurs, but it’s nothing to worry about.

On the other hand, there’s another nocturnal phenomenon called “sleep apnea” that isn’t so benign. During apnea you stop breathing for periods up to 20 seconds, and sometimes even longer — in extreme cases, permanently. Apnea is caused by a relaxation of the muscles that keep your airways open when you’re awake. To some extent it’s normal, and may happen 8-10 times a night. People with severe cases, though, have what’s called “obstructive apnea,” in which the tongue or even the tonsils can block the air passages. This can cause you to stop breathing as often as twice a minute, or perhaps 1,000 times a night. At best this means you get a terrible night’s sleep and go through the day exhausted; at worst you stop breathing altogether and expire.

Could this be your problem? Maybe — it’s estimated that a million Americans suffer from obstructive apnea. (Apnea is also thought to have something to do with Sudden Infant Death Syndrome, but that’s a whole different subject.) You wake up every time apnea occurs, but usually you fall back to sleep almost immediately and remember nothing the next morning. Other symptoms include bedwetting and morning headache. The treatment is pretty grim. They can cut a hole in your windpipe, or else give you a tongue-restraining device that you wear while sleeping. A less drastic alternative is something known as a “continuous positive airway pressure” (CPAP) machine, which provides a steady, gentle flow of air through a nose mask to keep your air passages open and prevent apnea.

Not crazy about these choices? Well, don’t panic just yet. Most obstructive apnea victims are hypertensive middle-aged men who snore and possibly drink too much. Usually I never miss a chance to be an alarmist, but this is one time I’d say you needn’t get too concerned.

Cecil Adams

Send questions to Cecil via cecil@straightdope.com.