Dzyhead Sam writes, in response to my vacuous challenge:
Your question: What are the fictional (invisible) books that are bad for a reader's mental health? The Necronomicon (and other Lovecraftian creations); the manuscript in Amis's The Information...
My answer: In Never Any End to Paris, by Enrique Vila-Matas, the narrator is trying to write a book (The Lettered Assasin) that is so good it will kill anyone who reads it. But! This is actually already a book by Vila-Matas. It's called La Asesina Ilustrada, and it hasn't been translated. Maybe because he SUCCEEDED??!?