Hi, tehp. Welcome to the board.
How old is your dog? Our 13-yr-old just had her first grand mal seizure a few weeks ago. It started out much as your dog's episode did--it looked as though she was being pushed from behind. In her case, though, it progressed to a grand mal seizure. We were luckily able to get her to the vet in time to spot some anomalies in her blood work, but past experience with another dog tells us that blood chemistry can normalize quite quickly after a seizure and show no evidence of abnormalities. So likely, the advice you'll get from anyone you see at this point is to wait and see if it was a one-off episode.
That being said, though, if you could post the video on some share site, like YouTube, you'd have a link to share. It might come in very handy if your vet should give you a referral to a neurologist--if the neurologist can rule out seizure from the video, it might save you a trip...
that it was just a one-time thing and won't recur!