I have a similar problem with the heart sensations. Sometimes exercise makes it worse, sometimes better. I believe it is something to do with the fight/flight reaction being overly sensitive. I have to just do some deep breathing, calm myself down, and lay low for an hour maybe.

I had the worst bout of this when someone told me some very hard news a couple days ago. My heart felt like it was going to explode right then and there. I knew it was just myself being overwhelmed and my body not reacting as it should. My chest was sore and my heart was beating heavy the next few days, but going for a run seemed to help stop the adrenaline rush in the days after.