Outside of this drill be in a position where you are comfortable and move to keep it that way. If you don’t want someone in your hitting range move or move him or find another way to do this (close the door or window…).
Stand at a comfortable hitting distance from each other and start fainting (hits that do not land) at each other with hits landing from time to time. Note when you feel the hit coming and how your body moves under this tension. Work to relax your eyes and to see more rather than focusing on the hitting limbs and after you feel your body is aware of the fear tension and is not following it blindly start to move to redirect the hits that are coming in.