Greetings.
Shortness of breath and feeling of heart flutters, needs an answer. I don't know in ER what they did. Probably they must have done an EKG and chest x-ray. But I think you require a Holter monitoring for 24 hours, which can record all the activities of heart in 24 hours time frame. If you feel any abnormality or symptom, you can press a button so the tracings can correlate the symptom and heart activity at that particular time.
You can read about holter monitoring here
I don't think they do a stress test or ECHO or pulmonary function test in ER. So you need to get that also done and see a cardiologist or an internist to give concrete opinion on your problem. May be just anxiolytic might be required but organic causes, like arrhythmia should be ruled out. Please feel free to ask, if you have further questions.
This communication is open till you are satisfied. I have 20 years experience of direct patient care as a surgeon, sports medicine specialist and a medical teacher. Please click accept if I had answered your question. Good feedback/bonus is welcome.