I agree with Vicki please check out AAI (Atlanoaxial Instability) GO to petplace.com and read about it there. I have seen AAI pups that are only 13 weeks old and it can be a congenital or aquired defect it is a defect of the cervical vertebra. It has many symptoms of LIver shunts and other problems and Hydrocephulas is usally another symptom of AAI.. I am also a very informed advocate of AAI where I am a parent of a pup that has it. His story can be read at
Dog profile for Wheelie Boy Babybear® , a male Yorkshire Terrier please check this out and see if you have seen any of these symptoms with your pup.