Should I be worried about a heart attack or stroke?

Well around 6 this morning i woke up and had really sharp pain under my left breast in the top of the rib. It hurt when I inhaled or moved, so i went to the ER. They said it sounded like it possibly could be a blood clot which can lead to heart attack, so they gave me an EKG and that was normal. Then they wanted to draw blood to check and see if it's a blood clot or not but i freaked out and refused to let them, not because im afraid of needles but because I'm afraid of bad news. I'm also 21, and ate mac and cheese and 2 twix icecream bars before i went to bad, so maybe it was just gas? the pain i was having went away when i was in the hospital but now im freaking out thinking "what if i DID have a blood clot...should i be worrying???