Yes, I agree with the last poster, I would see a doctor and get an EKG and echocardiogram done, as well as a chest x-ray, just to make sure it's not something with your heart or lungs. It very well might be something with the digestive system, though, my mom gets acid reflux and she thought it was her heart at first, sometimes she said it would feel like a heart attack. She sleeps a little bit propped up now and that solved it. My husband had side pain that radiated to the arm for years. The doctors didn't find anything wrong with his heart or lungs, and prescribed muscle relaxants to help. He never got the prescription for the relaxants filled, since he didn't want to just mask the problem. Well, he went to the chiropractor finally (at his friend's suggestion, he recommended a good one who is also an MD and orthopedic surgeon), and she took an x-ray, there were 2 vertebrae pretty far out of alignment, and that was screwing up his circulation. She adjusted him, and he was all better. It's been 2 years now, and he's only had to go back twice, she wasn't one of the ones that wants you to come in every month or anything, she said if it starts hurting or feeling funny again, come back. So, anyway, it could be something like that. But, don't let them just tell you it's something like that until they check your heart and lungs first, in my opinion.
Okay, this got longer than I meant for it to be, but I hope it helps a little!