Thanks for the post, godspeed. My doctor still thinks it's Acid Reflux and has put me on Omeprazole and tells me to take Gavascon after meals, before bed, and whenever I feel an "attack." The symptoms had gotten much better for several days, so I tried some light vaping again and was fine for a few days, but then had a rough patch of 2-3 days, so I stopped again, and am back to doing better. I'm still thinking it has something to do with a nicotine-induced acetylcholine imbalance, because Dramamine still seems to work best whenever I'm having an attack. I can take a Dramamine and I'm usually better within an hour. It's not just the "relaxing" effect, though, as I also tried one of my mom's Xanax, and it certainly relaxed me, but did nothing for the attacks. So it seems to be something specifically the Dramamine does, and I talked about its effects and its relation to acetylcholine/nicotine several posts ago. If you haven't tried Dramamine to help the attacks, give it a shot. It will make you drowsy, though.
It's strange you were still having issues even without nic, as there's nothing else in vapor that could conceivably make your heart race/pound. What I'm going to do is try to go a week or two where I'm doing OK, and then try vaping without nic and see how I do. I don't think it has to do with activity. I have played some basketball since I started having the attacks and I was mostly OK. I did have an episode once while playing, but it was minor and subsided quickly (it also happened long after I had gotten my heart rate up). Mine seems to be related to position more strongly than anything, because I'm worst when sitting in a certain recliner, so much so that I brought one of my porch chairs indoors and have been using it and have been much better. I have had some other attacks in different places: one in the shower, one woke me up while sleeping, one when I was on the computer at work, but the majority of them have been in the evening sitting in that chair. I have noticed, however, that most mornings when I wake up my arms are tingly/numb, as if it's a nerve thing.
I doubt it's a coincidence that we both started having these issues a few months after vaping. I certainly now think that vaping is either a cause or at least has an exascerbating effect on whatever it is. I'm still going to try to get my doctor to send me to a cardiologist to have some basic tests done, but I'm generally in a "very low risk" category for heart problems (young, no family history, not overweight, don't smoke, no high blood pressure or high cholesterol), so it either has to be something gastrointestinal related or anxiety/panic attack related. Whether the vaping caused it or made it worse, I'd still like to find out what it is.