What Cases Lightheadedness And Frequent Large Breath?

I'm 52 years of age and off/on for past year or so I get lightheaded, find myself taking large breath every now and then. Last week walked up a large flight of steps and felt like a huge knife was slicing my heart. Told friends who walked up steps with me and they said they had a hard time too, so I didn't worry about it. Since then a little ache in my left chest area and little numbness upper left arm at times (which I have had in the past). Never thought anything about it until I watched a special last weeked in regard to women and heart problems. My grandfather died of heart attack and 56 and "oh yeah" my mother (80) had heart attaclk couple years ago. My question is, am I over thinking this and making it worse? I know I should be tested, but what tests. I've heard of people having a heart attack EVEN after testing GREAT on stress tests?