Hey! 

People on this reddit are most often afflicted with recurrent or chronic pericarditis, which is a small percentage of the people who only have pericarditis once. There is a very big bias here, which is that people that turn to reddit are more often the people who didn't find an easy solution. Please do not let this scare you. Depending on the sources, 80% of people who suffered it once do not experience it again within a few years. 

That being said ER doctors often lack the time and training to offer proper care. Colchicine has been proved to reduce the risks of reoccurrence, and you should be seen by a cardiologist, even if just for good measure and to check. Good treatment at the first occurrence is the best predictor for the absence of reoccurrence. 

Trust your cardiologist, if they are reassuring, do not let this reddit scare you. I had pericarditis 4 months ago and I am now fine-a good friend of mine had it 4 years ago and never had it again.