I was wondering if you found out anything about the tests they did on your yorkie? It is good that they are doing the bile acid test. Yorkies esp small ones can have what they call Liver Shunt. My female yorkie was spayed at the age of 7 months and she is very small. (2.5 lbs) Then 4 weeks ago she had to have knee surgery for a luxating patella. The vet that did her surgery for that tested her for the Liver Shunt because she was so small. He said that if they have this that anestetia could be fatal because they can not metabolize the anestetic like they should. I hope things come back ok for your dog
Please let us know what you found out. I was not even aware of this disorder until she had to have the knee surgery. My local vet never even mentioned this to me. I am relieved that she did not have it. But the head movement is a sign of the Liver Shunt. Sounds like the vet you are using knows what they are doing
Best of luck to you. I know you must be worried sick. I know I worry about my little one. They are the best dogs so loving and fun.