Yep I panicked too. Even my almost 4 year old still does it to some degree. but my DS is a big jerker. It's funny but the Doc said to me it's because I spend too much time with him when he's falling asleep (not that he meant that badly) but sure enough, now he self settles, I hardly see it at all.
Both my DD and Ds have eye rolls, mouth twitches, leg/arm twitches, you name it! xo