My Primary Care Doctor Prescribed Propranolol For My Panic Attacks.

My primary care doctor prescribed propranolol for my panic attacks. I am a heart patient and am already on bystolic and tolerate it just fine. I have also been on .25 mg of zanax only when needed. For example, my 30 pills I got on August 1, I still have 4 left. My primary doesn't want to prescribe zanax, and yet I've been on it for 20 years. I just don't take it that regularly but when my panic attacks come, my heart races and it has been the thing that has slowed everything down. I had a panic attack today and took my first propranolol and have been upset in my stomach and diarrhea all day long. Starting to feel better, but should I even be on another beta blocker and how long does it take for this 20 mg of Propranolol to get out of my system?