Sheridan Hay, The Secret of Lost Things
Someone was behind Harold. He could feel it in his spine.
Rachel Joyce, The Unlikely Pilgrimage of Harold Fry
I don't recall ever sensing that someone was following me, perhaps because nobody every has, at least not in a sinister sense. Yet people do walk behind me, observe me from behind and sometimes walk up behind me and scare the bejeebers out of me. Unless I hear them or notice a shadow or a reflection, I don't sense anything.
So why do so many main characters in fiction get this feeling? And how come, when they are the ones doing the spying or the following, the people they are spying on or following never get this same feeling? This strikes me as laziness on the part of authors, a shortcut way of trying to give readers a chill sort of like that supposedly experienced by the characters. I just don't buy it, especially when one comes across it so often in books.
In real life some people really do sense that somebody is watching them or following them. I think we call them paranoid.