Sounds horrible. I can understand that stopping you from cycling, but if you could have managed to sit in a car, would you have been able to drive it? I can imagine that inner ear issues can sometimes affect vision too as my wife suffered from positional vertigo for a while and I could see her eyes flicking rapidly when she was getting dizzy. (I did find a helpful YouTube video about a sequence of positions to put the sufferer through which basically helps to remove the otoliths from the ear canal).

In my case, it was a brain tumor. Took a bit more than Lotus Position.

It all came out OK, in the end, but it was touch-and-go for a while.

Ouch!

Not quite a Lotus Position, but I used the Epley Maneuver on her which immediately lessened her symptoms: https://en.wikipedia.org/wiki/Epley_maneuver

When the vertigo is bad, you can't even go as a passenger in the car because the movement is literally sickening.

Even driving with mild vertigo could be difficult because you want to restrict your head movement.

Source: my dad gets Benign paroxysmal positional vertigo (BPPV)

I'd recommend him trying the Epley Maneouvre as it's quick and easy to do (needs someone to help though) and is unlikely to make anything worse.

Thanks. I've tried to encourage him to learn it. He's stubborn and isn't interested. He's had physio do it when he was hospitalized...

He's mentally sharp, and has a science background, but nope!