I think that high doses of vitamin c is a bad idea. I was on high dose c, up to 8,000 mg, for 7 months and became much worse. Finding the right amount of any supplement is important. And with AF your body is gonna be more sensitive, so start low and increase slow. If you take too much it can give you anxiety, headaches, nausea, diarhea. Make Sugar to take your b's and c's in the morning, lunch and around 3. Always increase the early morning dose first.
I'm currently taking 3,000mg. I gradually worked my way up to this. This feels good to me, but of course, like I said below, listen to your body. It will tell you how much to take. Personally, when I go above this I get insomnia.