Anxiety attack or heart attack?

October last year, I was at a movie convention. I was walking around the place when i began to get this pressure/tightness right in the center of my solar plex, like right below my chest bone. I began to sweat from my face and fear overcame me. I seriously thought I was going to have a heart attack. I had no pain in my arm or anywhere else in my body and I wasn't short of breath. I tried my best to calm myself down and after a while, the feeling went away. It happened again today while I was grocery shopping. Same exact feeling and everything. Are these minor heart attacks? I have no clue whats going on. Both these instances there were massive crowds, I dont know if that has anything to do with it. Ive never had this happen to me before. I dont know if I have heart disease. I work out regularly at least 5 days a week. Good hard workouts. No chest pains when working out.