Hey, im sorry you're going thru this. Idk if this might help but as soon as you enter the exam hall, forget about everything else and think only about the paper in front of you. As soon as you feel your brain getting distracted or foggy, slowly bring it back to focus. Read the ques slowly (I use my pen to underline key words), really ask yourself what is the examiner trying to test me on. You honestly might be really tired so have a good nights rest today it shoud help