37 year old male. had an episode of a fib a month ago. on meds for it but what can i do about the anxiety of it happening again?

Anxiety post cardiac: experiences is normal, especially re: engaging in any aerobic activities, including sex. Ask your MD for some reassurance as s/he knows your exact condition. In general, if your condition requires not exercising for a time, your MD would have told you. Meanwhile, learn relaxation techniques. This may have nothing to do with your actual heart condition but you'll feel better dealing with it