Why is my hr as low as 48 at rest? 20 yo male, normal size and shape, not an athlete. no symptoms, hr respond like normal with exercise. could i have heart block, sick sinus, or something serious wrong? just very slow resting hr no symptoms

Bradycardia: Normal heart rate is 60-100 bpm. Your rate,assuming EKG negative for heart block and a 24 heart monitor, should put your mind to rest, Additionally, get an inexpensive heart rate wrist monitor ( generic Fit-bit) and check your pulse 3 times/day. Keep a journal list date,morning, afternoon and late evening pulse and bring it to your physician. Without a confirmatory EKG cannot be sure.