I did an exam that had an oral part. The brain fog really sucks, I didn't care for my stutter at all, I was just nervous about not knowing the answer. I passed :D But the brain fog was so intense it felt like I was weeding through a fog from my nerves trying to remember that which I otherwise would know so well. It's like the mind was just going blank at the smallest things. Don't worry about stuttering, just study and know the material :-)