Does he have a fever? Also seizure are defined as lasting quite a long time - like a minute or longer - something like that. When my daughter was 11 we were out at a corn maze wtih a bunch of friends when she came up to me, said she didn't feel good, put her arms around my neck and fell backwards like a ton of bricks. While on the ground she seems to have a seizure. When we saw a neurologist he asked how long did the tremors last? I counted off in my head about 8 - 12 seconds - which seemed like an eternity at the time. That's when the neurologist told me it wasn't a seizure - but jsut some involuntary movements made when a prson passes out.
To date we haven't figure out why she passed out that day - low blood pressure? low blood suger? We went to the ER and had a complete work-up - nothing. It's been 4 years and there have not been any events like that since.
The fact that you got it on video is excellent - show your doctor. It could be that he'd going through some development stage and he's experimenting with how things look, feel, sound when he moves his head this way, or that way, etc. Or he could be dealing with low blood sugar if it only happens when he's waiting for his meal. We moms let our imaginations go crazy and we project all these worse case scenarios.... Don't do it!