You're describing involuntary muscle twitches known as hypnic jerks, sleep starts, or myoclonic jerks. They're very common; most people experience them from time to time, but we really don't know what causes them. One theory holds that they're a part of the general slowdown of the nervous system that occurs as you're falling asleep. Your breathing slows, your temperature drops and muscle tone changes. Hypnic jerks, this theory goes, occur as a result of the muscle transition. Another theory holds that just as you're drifting off to sleep, your brain misperceives all that relaxation as a sign that you're falling, and alerts your arms and legs to stay upright. While the physiology of these involuntary movements remains unknown, we do know that you're more likely to experience hypnic jerks if you have poor sleeping patterns or have been sleep deprived.
Because hypnic jerks are considered medically harmless, there's not a lot of research on them. I found only eight studies in a medical literature search - the most recent was published in 2007 and was just a review of the differences between various sleep-related movement disorders. Most of the others were related to children.
I suggest that you consult a sleep expert. The solution may simply be better sleep hygiene - steps you can take to eliminate obstacles to sound sleep. Here are my general recommendations for getting a good night's sleep:
- Check your mattress for signs of wear at least twice a year, and consider new pillows if yours aren't comfortable. A worn-out mattress (or one that doesn't suit you) can contribute to sleeping problems.
- If your bedroom is noisy, buy an inexpensive "white noise" generator that makes soothing sounds to relax you and mask any noise that may be disturbing your sleep.
- Try my relaxing breath to help banish thoughts that are causing sleep deprivation.
- If you get up frequently to urinate and can't get back to sleep afterward, try to eliminate caffeine and alcohol. Don't drink beverages containing caffeine or alcohol within three to four hours of bedtime.
- If you can't sleep, get up and read or do some light stretching. This may take your mind off the problem of not being able to fall asleep and help you relax so that you can doze off.
- Consider using the natural sleep aids melatonin or valerian occasionally.
Andrew Weil, M.D.