Everytime I Exert A Mediocre Amount Of Energy. My Heart

Everytime I exert a mediocre amount of energy. My heart races. When I lift weights. My heart races so much and it just doesn't feel right. Like it doesn't seem like it used to do that. But it could be that I never cared to notice. It's important to state that I have been battling anxiety lately really bad. And panic attacks. I've had bad anxiety attacks after running and I finally went to the dr. Ekg/blood/urine/blood pressure all good. Lungs are fine as well.
I did sprain my back recently from over stretching. And that's causing a lot of pain in shoulders and middle back. But that seems to be the extent of what the dr's are saying. And that its my anxiety.
But like just a second ago. I went to help a friend jump start his car by pushing it down a hill so he can use the manual start. I literally pushed it for 10-15 seconds. Something that isn't that big a deal. And my heart goes racing. I didn't panic. But I hate that it's beating so fast for nothing. I am a former track athlete. But I haven't been working out that much lately and I am definetly not in good shape.
My question is. Should I just push through it and continue to workout. Do you think it's just that because I'm anxious lately I'm over paying attention to my heart beat?