I had the same experience with leaf parsley as a kid - my aunt made a broth with a bit more parsley than I was used to, and something - probably unrelated - made me almost vomit then. My brain "connected the dots". From then on, pretty much just seeing leaf parsley would make me nauseous, and I was quite a PITA for the family over that. 10-15 years later, something "clicked" in my head, and now I actually like it in my soup.