IF you have low cortisol, high dose vit C will lower it further...
That's why Lam mega-doses vit C with people in stages 1,2 AF who usually have high cortisol to help bring it down, get adrenal balance etc..
So jumping from 2 - 6g if you have low cortisol could make you feel even more fatigue, nausea etc.
I went from 1g to 3g and couldn't walk straight, had no balance, and fatigue was even worse than before.
See how you do but i would not jump from 2 - 6g - i would slowly taper up.