I am not a doctor, but when you already have low blood pressure and given a med that causes it to go lower.....I would have googled the side effects before swallowing or paying for a pill. And then asked the doc why, I believe you fainted because of the too low blood pressure caused by the med. I would wean or get off the med. Not twlling you what to do, but what I would do.

Then I would get off anything that can cause or make afib worse which is anything with caffeine in it and high sugar diet.