I had costochondritis a few years ago. It's cool because every symptom is IDENTICAL to that of a heart attack, but it's completely harmless. Can't breathe, feels like someone sitting on your chest, numb back and arms, etc. It lasts for weeks and sometimes months. Rib cage cartilage inflammation, I was lucky because it only lasted about a week for me. The treatment is basically "take some Motrin, try not to breathe much" and wait it out.
Being human is a pain in the ass. It's bad enough our minds are fucked up most of the time, but then our bodies turn against us too. THANKFULLY OBAMACARE WILL SAVE OUR COLLECTIVE SICKNESS.