(HealthDay News) -- Ever wonder why your body sometimes jerks just as you're falling off to sleep?
The answer is a phenomenon called "sleep start," the Nemours Foundation says.
While no one quite understands why sleep start occurs, the theory is that the brain misunderstands the natural relaxing process that muscles go through just as you drift off to sleep.
In response, the brain orders the muscles to suddenly tense up to prevent a sensation of "falling."
Whether these sensations wake you up or don't disturb your sleep at all, experts say they're nothing to worry about, the foundation notes.
