What Causes Rapid Heart Rate After Exertion?

HI!
I’m 29 year old male and in good shape. I used to be really active before I turned. Played soccer games multiple times a week (lots of running) and did bicycling 30 miles per week. When I hit 20 other things came in the way and I completely stopped. However, I still have a demanding job 10h a day where I physically lift 100lb on a regular basis and walk at least 10 to 15 miles a day. Three months ago I thought I would go back to biking and wanted to get in shape with stationary bike first. Everything was going good but two months into the training I become aware of my heartbeat at night as well as sudden adrenalin surges that kept me awake. My heart rate remained the same but my heart felt like it would jump out of my chest. That was happening even two or three days after cardio workout. I am not new to sports and exercises and I don’t think I was doing anything wrong or overdoing it. My blood pressure is OK. I quit the workout completely and things become better over the next two months to where I don’t have the adrenalin surges anymore and my heartbeat isn’t as powerful but is not gone completely. It has reached a plateau but now my heart rate goes up with a little effort - physical or emotional. I’m not a type of a guy who worries and I am tempted to just go on with my life pretending that everything is fine but would that be smart idea? I mean, could it be that somehow I damaged my heart or related parts by overstressing them and now my heart has to work overtime for even the little efforts? Is that likely or would everything return to normal after some time and if so how long? Also, even if things go back to normal again how would I return to biking w/o causing it? Please help!
THANK YOU!