Where to draw the line between imagination and insanity?

It's really a harmless book that Manuel is reading: the story of a mad axe murderer. A fictional story...or perhaps not? He is hypnotized by the text, drawn deeper and deeper into the reality of the tale. Suddenly he sees absurd pictures, pictures that have something to do with his past. As he begins to understand their meaning, the boundaries of reality shift. It is too late. A never-ending nightmare has begun.—derwandlerfilm