I do not want to go against the good advice others have given you, but to, perhaps, ease your stress a bit, I just want to mention that I went through a period of similar pain back in my twenties, when I was playing drums professionally. It turned out that sitting crouched forward night-after-night, slugging away at the tom-toms had gradually bruised a muscle in my chest, causing scar tissue to form and leading to horrible, recurring pain in my chest, exactly as if someone had punched me in the breast bone.

After a few weeks of anti-inflammation therapy and several months of re-adjusting my drumming position, I was able to play virtually pain-free for a number of years after that. Again, I don't want to be the guy who talks you out of going to a doctor for chest pain. I'm just suggesting that the pain might not have anything to do with your heart or lungs. Get it checked out.