I'm going to give you a response which will seem a bit lateral to what you raised - but you never know, it might give you a clue as to why the treatment for vertigo didn't work and the motion sickness pills sometimes do and sometimes don't.
If you find travel stressful, then what you could be experiencing is a combination of blood pressure rising and blood sugar falling. Why I mention this is..........
If I am in a meeting in which I run adrenalin, I find that after about an hour I get dizzy, i.e. the room gently rotates or sways from side to side.
The cure? Raise my sugar levels by snacking a mixture of a high glycemic index bar plus something with a medium/low glycemic index. This takes about 15 minutes to stabilise the room
I also consciously try to calm down As I take a beta blocker for hypertension, I don't actually know when I'm worked up and running adrenalin so I have to imagine that I am and then calm myself down!