Sound like anxiety or a heart issue at 21- just got home from ER?

Not to scare you in the least, because it's certainly EXTREMELY uncommon, but a woman I used to talk to explained to me she had a heart attack when she was 20, and 3 times up to that point (she's 33) Heavy anxiety can cause a lot of things that shouldn't happen. But I can relate to you. I'm a very anxious person and sometimes I feel like I'm going to have a heart attack or die, and it helps a lot to breathe and focus on something else until that feeling goes away. If you continue to think you're going to die or anything related, then you're going to start seeing more symptoms. It's all mind over matter.