A little late to the party...
Another thing to consider (and this isn't to unnecessarily scare anyone, either)...my older brother and I both have Tourette's Syndrome. His is very pronounced and one of the things I remember about him as a child is that he would sit watching tv and shake his head back and forth every few seconds. As an adult he has a number of tics in his face, he twitches his shoulders and knees and things like that. It's not a harmful malady, just annoying and embarrassing for him as a child.
As for me, I remember having a number of compulsive behaviors until I was about 6 or so, and then I grew out of it. My mother also has TS but it's confined mostly to her mouth and her hands and not very severe at all.
Of course I'm hoping that it's just kids getting their synapses wired correctly and all that, but I thought you'd like the info.