Dogs really do not do well with a vegetarian diet so I'd not do that unless directed to do so by your vet.
This sounds like there may be a neurological issue going on which could be due to a liver problem or might have its source in the brain, the inner ear, or the spine too.
Disc problems in the spine are seen in this breed. You can read about disc disease here
http://www.veterinarypartner.com/Content.plx?P=A&A=2373
He may be showing vestibular disease due to inner ear infection which you can read about here
http://www.marvistavet.com/html/body_vestibular_disease.html
You can read about liver shunts in this breed here
http://www.bhejei.com/health-pss.htm
If blood work doesn't find the problem for you then you may want to consider neurological issues as a next step to investigate.
As this might be a neck problem you might try going to a harness for walks if you use a collar now. Might be pressure on the collar is putting pressure on a disc in the neck resulting in what you see.
Hope this helps you!
Dog Expert:Rescue, Train,Breed,Care
30+ yrs dog home vet care & nursing, rescue, behavior&training, responsible show breeding, genetics