I think hydration can definitely play a role. There have been times when I get a flare up and I go through my basic checklist, did I eat enough today, too much, did I get enough water. Usually I haven't had enough water, and I get a glass, and things settle down. I don't know if it's related though.
Well, that is interesting, if they literally stopped when you got the IV fluids. I know nothing about ER medicine, but sometimes the baggies of fluids have either sodium or potassium in them. Again, I know nothing about ERs but sometimes the IV is standard procedure (for a variety of reasons), and also to allow IV medicines to easily be dispensed if necessary.
Staying hydrated, and making sure you get enough potassium and magnesium in your diet can sometimes help calm PVCs. Magnesium can be taken in supplement form (magnesium citrate, and others) but potassium really should come from food sources (like bananas, etc). Apparently sometimes many people get magnesium deficient and don't know it.
I've had this happen before. I had a similar thing happen at my ER trip recently.
I can't comment on aerobic training, but when I do heavy squats, they seem to bring out PVCs (and very bad ones, and even a run that sent me to the hospital last time). I couldn't even begin to give an informed explanation of why, but I know that heavy squats, particularly, do that in me (and have before as well).
that's the very nature of the buggers. They come and go. I've not been able to correlate it to anything.