It's common to be fearful of the heart after having svt. It is a scary thing to go through but odds are it is cured. If it turns out it isn't then a second ablation usually does the trick. And also, if it isn't not exercising isn't go to stop it from happening again anyways because svt, with the exception of afib, is caused by extra muscle fibers in the heart and those don't go away simply by not exercising. So just try to breath deep and steady when you work out. Try to calm the fear and slowly build up your intensity. Learn vasovagal maneuvers just in case you do get the svt back. Holding your breath and bearing down like straining to go to the bathroom. Drinking a cold glass of water. Coughing or jumping up and down. Maybe if you have a few tools to get it to stop you won't feel so out of control. In any event, no one can tell you how to get past your anxiety over this. Sometimes we have to just face it head on so it doesn't take over our life. Maybe think about speaking with a counselor for a couple of sessions to work out the anxiety. Take care.
You can do what I did. I had my cardiologist give me a stress test. He administered the test, and kept pushing me until I punched out totally drained, and drenched in sweat. This set my mind at ease that I could safely hit my personal limits with no SVT, and really gave me confidence that there was no more SVT.