Never smoked and didn't work with chemicals.
We were dissecting my diagnosis down at Norris--could it have been parasites from years in South America?--and Dr. Stein said "Sometimes it's just bad luck."
Progress is almost always two steps forward, and one step back. But you can't move those two steps forward if you're busy kicking yourself for what you may or may not have done in the past.
(Clara--this wasn't really directed at your question, which was a valid one. I just wanted to make a point about how much perfectly good time we can waste second-guessing what had already happened. As Sigmund Freud may or may not have said, "sometimes a cigar is just a cigar." Not necessarily a smoking gun.)
Afterthought: The only person I can think of right now who should be kicking himself every day is probably this guy:
Bonus points if you recognize him and know why those kicks are much-deserved.