If possible/allowed by the guidance you doctor has given you, take both medications before the flight, timed to give the maximum benefit - then believe they will help and that most likely you didn't even need to.
Enjoy your flight.
If you've got Xanax, then I think you're probably covered. I've only had afib once but I was very nervous flying the first time after it happened (and I get nervous flying anyways). The Dr prescribed Klonopin for anxiety which is another benzo similar to Xanax as you probably know. After taking that, I wasn't worried about anything and had a great flight.
The chances of afib while on the flight are extremely low. Even in a worst case scenario, afib is not a life threatening condition and it's a relatively short flight so there is no danger involved. There's no reason to worry and the Xanax will help with that.
I agree, take your Xanax and BB beforehand and you'll sail right thru. Don't overthink it. If you've made the decision to go, go and enjoy your trip. Afib may make us crazy, but it will not kill us. We should not let it rob us of the joy that life has to offer. I am a fellow afibber, so I know the anxiety it can provoke. I went on vacation last October for the first time in 2 years because I feared afib. I did fine and you will too. Hang in there!
I used to hate flying but I really enjoy it now. I had to start flying a lot for work and I got used to it. Time will go so quickly.