I'm not sure why you have antibiotics. Is it for another problem? Vestibular disease is not treatable with antibiotics unless it was miss-diagnosed as an ear infection. Otherwise the dog can be treated with medication (not antibiotics) to help control the dizziness.
As for the eating, how old is your dog. Vestibular disease usually affects older dogs, and not to sound harsh, but maybe this is your dogs way of saying she's tired.
When a dog is suffering from this disease it is important to control the dogs ability to roam. In serious conditions it is advised to always walk the dog on a leash, even indoors. And remain calm and quiet at all times for the dogs sake, so as not to confuse him.
It sounds like the dog is in a serious case if it has lost all peripheral vision, and lost his ability to control his movements, more importantly if he can focus long enough to eat.
i hope that helps a little. Good luck.
