I am 31 in a month and have had 3 episodes since around the age of 18
All 3 were caused directly and immediately after vomitting.
Case 1: Dehydrated, played baseball, got a migraine, threw up - heart was beating fast, didn't know at the time I had a-fib until I woke up and my heart was still racing.
Case 2: Drank a lot, vomitted, immediately heart went into a-fib
Case 3: Drank a lot the night before, woke up feeling ok, then felt nausea. Threw up and then went into a-fib.
Quite honestly, it's been about 5 yrs since that last case and I don't think I've thrown up since then. I am actually now afraid of vomitting purely because of the fear I have of going into a-fib as a result.
My suggestions: Keep away from caffeine (all of it), limit alcohol intake and keep hydrated if you do drink. Keep hydrated in any type of heat/sports.