I Used To Run 5ks Then I Started Suffering From

I used to run 5ks then I started suffering from anxiety and found that when I exercised I felt worse, I would get chest pain, the shakes, sweaty palms and feet and just feel terrible. I visited my cardiologist to make sure nothing was wrong with my heart, as I suffer from mitral valve prolapse and my family has a history of heart disease. He recommended that I take a stress test, as well as blood tests that would check my cholesterol, and how my heart was functioning. They all came back with great results, saying I was below average for heart disease. That was about two years ago. I took a break from exercising after I got those results and recently this month I've started running again. As I exercise I get chest pain and feel very weak afterwards. To the point that I just want to lay down and rest. Also my heart takes a while to return to beating regularly, and I can feel it beating even after I have showered, and cooled off from exercising.

My question is this. Could two years of not exercising really make a difference with regards to how my heart was functioning before, so much so, that I could have developed angina or some other heart problem? I've been getting a lot of headaches and shoulder pain on my left side as well.