I don't have time to give you a long answer, but that sounds exactly like what happend to my mother. After many scans, ear cleaning, doctors etc etc, nothing helped and she only got worse. Is your grandad on Warfarin or other medication? I can't remember what the other med is called that my mum is on, but they changed it to another one and that improved things. We went to a chiropracter who fixed her back up, and that helped the problem about 35%, then we went to a nutritionist, who put her on a better diet and some supplements for vitamins and minerals she was deficient in (by blood work), and now, after her having the problem for 3 years (she had to crawl sometimes from the lounge to the bedroom because she was so dizzy), she is 100% better! She can even work out in the garden again, and says she hasn't felt so strong in years. I would say try looking at those things for your granddad.