I posted in that thread - saw a cardiologist and they confirmed it. In retrospect, it was probably the worst illness I've ever had, being completely out of commission for a month at age 29, where even doing simple things like rolling over in bed would cause my heart rate to spike and cause me to be short of breath. Couldn't do anything but lay there. Luckily a scan confirmed no long term damage.

For some reason still decided to get the third booster.. and I still ended up getting COVID twice (very mild both times). Don't think I'll be getting any more COVID vaccines.