At the moment you dont know anything about your cortisol, you dont even know if cortisol is a problem. You can have AF without neccesarily having a bizarre cortisol curve. so i wouldnt do anythng other than vitamin c and b5. What your referring too is most likely adrenaline, not cortisol. Its 95% the case normally.
Meditaiton, sleep hygiene, vit c , b5, milk thistle...all the basics till you have your tests done.