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.