Stilton - have you had an appointment with a Neuro-otologist yet?
If you see one with the right kit, they'll be able to diagnose you in an afternoon.
If you can get to London, the place you want to go is the Royal Ear Nose + Throat Hospital in King's Cross. Having been checked out there myself, it made me realise that there's absolutely no place for anyone other than the very top-flight pro in getting a diagnosis of an inner ear issue.
If you're based in England, get your GP to refer you to the Royal ENT pronto - it'll put your mind at rest, I promise.