As a first responder (ski patroller), I'd advise you to get in to see your doctor immediately. Here's the thing - it could be nothing but then again you could be looking at serious problems. You'd want to find that out in the doctor's office not when you drop over from an MI while riding. The potential for a serious problem is relatively low but the potential for catastrophe if it is real is very high. It's often the case with heart and brain issues (stroke, concussion) problems for the patient to be in denial and to want to avoid treatment. There are many cases of just such behavior where the patient avoids and then winds up in serious trouble or dead.

The other fail here is going to a biking forum for medical advice.

J.