The bit of problems I have had with Vestibular issues I can tell you it's not fun. I was suppose to go through physical therapy for Vestibular issues but my Chiropractor fixed the problem and I never went.
Maybe a far stretch but would he be willing to go to a chiro to get checked out? Dr. are never happy when you tell them that you go to a chiro but I don't care.
My vision wouldn't focus and I would get super dizzy, get the spins at night ( which sucks when you're drunk but is worse when you did nothing to deserve it!) I couldn't ride or teach my lessons.
When I went to get adjusted I told my Chiropractor what I was experiencing and he took some x rays. Turns out my neck was to straight ( there is suppose to be a slight curve) most likely caused from my horse the few weeks before. He adjusted me and my vision instantly focused. Weirdest feeling ever. After that the spins stopped.
From my own personal research and experience (I am not a medical professional), Meniere's is a label for a collection of symptoms relating to specific inner ear symptoms -- it's not an actual disease. After seeing multiple specialists and having every kind of test they could think of, I was diagnosed with Meniere's because they couldn't figure out anything else to call it. My symptoms were intermittent, but when I had them, boy, was I miserable. nlk is right, they are NOT FUN. There is no cure, and the treatments are only designed to alleviate the symptoms. None of dietary changes and anti-vertigo drugs/supplements did anything to help me.
After dealing with tinnitus and vertigo attacks for years, I started seeing a chiropractor and mostly eliminated gluten from my diet (gluten is an inflammatory agent), and I have been 100% symptom free (knock on wood!) for several years now.
My sympathies to your dad -- my best advice is to be persistent and try alternative solutions if he can't get relief from the medical options.
My husband has/had it and it was not fun. He would lay on his back perfectly still until he really, really had to go to the bathroom, attempt to get up and (literally) crawl to the bathroom, or fall down on the way. Kinda spooked the kids!
I found an ENT in Charlotte with an expressed interest in Meniere's who put him on a Very low sodium diet (1000 mg/day) and a mild diuretic (triamterene), saying that patients who were compliant usually got the attacks down to 1 per year. My husband hasn't had an attack in about 4 years, and has eased his sodium restriction slightly (1K is tough to attain) without ill effects so far.