I have scopophobia, the fear of someone behind you or watching you. I tend to notice anyone behind me, I just feel it on my back. I never feel comfortable with my back in the open or in a crowd, I always have to have my back against a wall where I see everything. This fear has actually kept people from doing jump scares from behind as a joke or for Halloween. So in conclusion, because of me fear I can feel or notice someone behind me.