This sounds like it could be either a partial seizure or a movement disorder (paroxysmal dyskinesia). Unfortunately at this time there is not a specific diagnostic test for either of these conditions - it is a matter of excluding other possible causes.
If I were you I would keep a diary of everything connected to Sable so that if she has a further episode (and fingers tightly crossed she doesn't!) you may be able to identify any possible trigger. Also, if it happens again try to video the episode so that the vet can see exactly what is happening - although I know that making a video is not the first thing in your mind at such a distressing time.