I am sorry to hear you are experiencing the weird heart sensations.. I was having that for a few days around Christmas time, and it freaked me out. I usually don't get those flip-flop feelings, but kept getting them off and on for about three days. Along with it, I kept feeling very weak, not well, somewhat short of breath, and lightheaded. It even caused me to end up having another panic attack the other day (which I haven't had for a long time). I don't know what the cause exactly was, but I still feel as though maybe it was related to either holiday stress, or having a mild stomach bug the day or so before the heart thing started. It is so odd, but ever since I started having lupus symptoms (about five years ago), I get "sick" after I've already been sick, and gotten well, if that makes any sense. I will feel better from whatever illness I had for a few days, then all of a sudden for the next few days, will keep feeling those light-headed type of symptoms, along with the heart thing.
By the way, I was curious what type of effect Plaquenil had on your body? I have been on it for over two years, but just recently had the doseage increased, and now have been getting a lot more anxiety and heart palpitations (racing) since I did that. It has been two months since the increase, so I was hoping maybe it would subside, but I keep having problems with constantly feeling anxious and unstable.. I'm wondering if that has anything to do with why you went off the plaquenil? Did your doctor suggest a substitute possibly? I hope you are okay.