Maybe it may not be beating like this throughout the whole day, just the few minutes you may feel the anxiety. You should be fine.

Since you work cardio it's a good thing. I should also add a lot of things can factor into heart condition, like cholesterol levels or family history..

Atrial fib is extremely common, people live with it not knowing they even have it, it can cause issues but chances are low.

Everyone has a baseline in heart rate just like BP. The chart you may see are just standards for the general population. If you know yours, taken at the same time every day not after exercising etc. you're good