Most people who are having a heart attack attribute their discomfort to indigestion, stress, panic, or some sort of sensory or physical overload from work or family issues. Most who are truly having a heart attack deny they are having a heart attack when the warning signs occurred. Most feel an impending sense of doom.
Yes, shortness of breath, diaphoresis (intense periods of sweating), pain, nausea/vomiting, jaw and neck pain, and shoulder pain may or may not accompany heart attack. It may not follow the textbook pattern.
But recurrent substernal pain (pain below the sternum) is not normal. Yes, it is may be Gastrointestinal in nature and may be nothing more than Hiatal Hernia. But it is always best to be checked out by a licensed and qualified doctor.
Heart disease is the biggest killer in America today. Most people that collapse and die from MI (heart attack) die outside of the hospital setting.
Do you smoke? Have you had a physical work up recently?
It is good that you are physically active, yet, I have taken care of physically active individuals in the intensive care unit that had not a clue about their health and felt that they were knowledgeable people. Unless you have a complete physical workup, you are playing with fire.
I know you do not wish to hear it, however, a person who diagnoses themselves, has a fool for a doctor.
It is worth checking out, or you just may unexpectedly "check out."