Could be lots of things, something like a neurological or skeletal problem, seizure for some reason, a hypoglycemic episode which can happen on it's own or due to an underlying problem, a genetic disorder of some kind, idiopathic head tremors or all sorts of things. You should discuss it with your vet, if your pup has another episode before you get in see if you can video it with a cell phone or something so your vet has a more accurate idea of what you are talking about. Hope it's nothing too serious.
www.americanshihtzuclub.org
www.americanshihtzuclub.org
