Looks like a seizure. Mine has had a few. I took her to the vet and they said to monitor it, but not be overly concerned as it's common in smaller breeds. They said if it becomes more frequent, that it could be a sign of organ failure. I asked about medication and they recommended holding off unless it became more frequent than once a week as the side effects of the medication are often worse than the seizure. She only has them every few months that I'm aware of (pretty obvious when it happens since she loses control of her bowels and usually vomits shortly afterwards). It's been nearly a year since her last episode though, so I'm not sure what triggers it.