the truth about truth serum?

I just finished listening to the audio book version of "lunar park" the latest novel of writer Bret Easton Ellis. I really enjoyed the book even thou it left me rather confused on what did actually happen and what was fiction? as this is set up as a biographical book with Ellis himself as the main character, transforming into a Stephen King like horror story with a haunting house scary toys and fictional characters brought to life. I don't think I've seen a novel like this before where you in the end have no idea if anything you just read is true or not. you should read it and decide for yourself. :)