I'm no expert on vestibular stuff, but I did have vestibular lab testing, including the goggles thing. All they found in me was a little positional nystagmus when I lie on my right side. Nystagmus is "beating" of the eyes, where they flick back and forth, attempting to correct for missing or scrambled balance signals. It is considered "consistent" with having a neuroma on the balance nerve.
That "put me upside down in various head postions", followed by a serious bout of vertigo, sounds more like the issue where stuff (crystals? flakes?) gets stuck in the semi-circular canals (more like tubes) that make up your main balance organ. I think Dr. Mattox is right, it is probably not directly related to the AN. I also think, based on casual conversations with the therapist at the vestibular lab, that the therapy is often quite effective at clearing out the tubes so they can function properly. Once they get it cleared out, that is. Sorry it has to get darkest before the dawn...
As far as surgery, I think they basically just take out the balance organs on the affected side. After some weeks, your brain adapts to having balance on only one side, and you can do fine again, as long as you are not in the circus. I believe that the organ also comes out in the standard trans-lab surgery for ANs, or at least the nerve is cut, which has the same effect. I'm hoping the vestibular therapy will do the trick, though.
Take care. PS, it has snowed, of all things, over the last couple of days. Only a few flakes, but come on, the tulips are up and it is almost May!
Steve