I was in my later 20’s when I started noticing I was adversely affected by motion…I noticed driving got more difficult as there was too much movement between cars, guard rails, trees etc…I also noticed walking even caused the lightheaded, balance issues…it’s gradually gotten worse ( I’m 62 now). I never got an explanation of what was wrong. Then neuropathy started 8 yrs ago which just exacerbates it…unpleasant to deal with.
Similar to you it gets magnified in big stores etc….I think we fall into getting agoraphobia…which isn’t a surprise when you’re uncomfortable with your surroundings because your vestibular system is broken.
And that just throws gas on the fire. You’ve probably noticed pushing shopping carts provides some mental security. Best wishes to you .
Steve