[Ellie May]

I'd just have the vet take a look. No reason to panic.
If you can't get a video, you can just explain it. Sounds like what is called a play bow..but not all dogs are playing when they do it.

Generally these kind of symptoms are caused by either stomach prolems or spinal problems. Lack of appetite can go along with either. Because yorkies have weak intestines, that is likely the problem. Or maybe it is nothing at all. But I can tell you that my dog has extensive spinal disease and when she is sore, she does this after eating. It can most definitely be a symptom. She does it a lot when first waking up too...