I have a friend who's done ayahuasca a few times ("a horizontal experience") and recommended it. He did it in the UK. But I don't know, his experiences sounded like a really bad LSD trip to me. Not sure I'd like to go there, especially with all the vomiting.
edit: I'd like to add that I also have terrible anxiety, which has gotten worse over the years. I get panic attacks, sometimes out of nowhere, but yeah, not sure I'd go this down route... maybe it'd be just the thing, but makes me freakout thinking about how terrible it could be.