I can share a story about heart palpitations: I started having them in ~2008 without any previous infection (that I know of). Interestingly enough, they were appearing when my heart rate was going down - most noticeably while I was lying in bed trying to sleep, which isn't easy if your heart starts "missing some beats" out of the blue! Went to various doctors, they couldn't find anything wrong with my heart, but couldn't find anything that could help me get rid of the palpitations either. Then, in 2010, I got chickenpox, which at age 36 is a pretty big deal, with high fever, blisters all over the body etc. That took two weeks, and after that my palpitations were gone, and haven't returned since (knock on wood, fingers crossed etc.). So I can only assume that I had some form of myocarditis and the high fever got rid of that too?! No idea...