I read a short story while I was studying in Mexico, so I am almost positive that it was a contemporary work by a Hispanic author, about a man sitting reading a book one night ( I for some reason believe it was dark and maybe stormy and that he was sitting in a chair reading by a fireplace). He is reading about a man reading a book, and outside the character’s window there is someone lurking. The story ends with the reader hearing a noise outside his window, insinuating that he himself is the character that he is reading about at the exact same time.
I’ve been searching for this for ages as well after reading it on a creative writing course several years ago. I finally discovered it this morning and I think it may be what you are referring to: Julio Cortazar’s Continuity of Parks. http://www.continuityofparks.com/by-cortazar/