The Double- by Jose Saramago
Tertuliano Máximo Afonso is a divorced, depressed history teacher. To lift his spirits, a colleague suggests he rent a certain video. Tertuliano watches the film, unimpressed. But during the night, when he is awakened by noises in his apartment, he goes into the living room to find that the VCR is replaying the video. He watches in astonishment as a man who looks exactly like him-or, more specifically, exactly like he did five years before, mustachioed and fuller in the face-appears on the screen. He sleeps badly.