You need to go to the ER because this could be a heart attack, PE(blood clot in the lungs) or respiratory problem like asthma or pneumonia. Or it could be acid reflux or something simple as a pulled muscle. No matter what it is you need to have the life threatening things ruled out. You probably should call 911. If you are young and not having breathing problems you can choose but if you are having breathing problems or in your 40's or older take an ambulance. Time means loss of muscle. If you are having a heart attack every second you delay means loss of heart cells.