Yes, you mentioned some other things we have in common. I don't drink, either. I've never even tried, as a few close relatives have had very bad reactions (especially to spirits), and I'm not even Asian that I know of unless you count one great-grandfather born in the Philippines.

I also think I have a slight reaction (though not as torturous as yours) to exhaust fumes, even with a gas-powered chipper/shredder I was using last summer. Since my reactions aren't as severe as yours (I don't get the heart reactions you do, though that type of symptom is recognized in 'Asian flush' so to me it makes sense in a way), and also delayed, sometimes I just accept that stuff needs to get done and I'll just suffer later.

One sort of ironic thing is that I used to sort of roll my eyes at the idea of perfume sensitivities etc, which is an attitude I picked up partly from a grandfather who worked with petrochemicals and other dangerous substances his whole life, as a mechanic and machinist, and also suffered often from terrible migraines---and died soon after 50, of leukemia.

Sometimes I wonder if people who have a more immediate physical reaction to chemicals may be sort of 'canaries in the coal mine' as far as carcinogenic substances go. I wouldn't be surprised if some of these things may be linked to cancer and neurotoxicity generally.
Although I'm still stuck on (read: infatuated with) my theory about some of the aldehyde dehydrogenase enzymes and/or other enzymes perhaps playing a role in at least some individuals, I did come across this page that addresses some other explanations:
https://www.geneticlifehacks.com/multiple-chemical-sensitivity-mcs-genetics-causes-and-treatments/
Thank you again for your sharing and helping me with this!