Thanks for your query at DoctorSpring.com
I understand your concern
I have noted your symptoms. You are having Mobitz type I second degree AV block. This is relatively benign condition compared to Mobitz type 2 block which is a more severe variety and may progress to complete heart block. Still there is small percentage of patient in Mobitz type 1 block (infranodal variety) which can also progress to more severe heart blocks. So please upload your reports for further evaluation. I agree with your doctor that this could be (if type 1, 2nd degree at AV level) a benign condition , because there is no progression but since you have symptoms such as dizziness (which occur due to skipped beats and reduced blood supply to brain and blood pressure), Intense workout increases work load and oxygen and blood demand of heart and may precipetate syncope and dizziness, so he has adviced to avoid intense exercise, though you can continue moderate exercises.
Hope it was helpful
Feel free to discuss further