Reminds me of The Dark Half (spoilers)
Spoiler Warning *****
Secret Window and The Dark Half. Two Stephen King stories involving a writer w/a serial killer alter ego drummed up from his subconscious and writing style. Both John Shooter and George Stark also share similar southern lineage and determination to alter the writing. Personally, I find The Dark Half to be a far superior book and film (the adaptation is surprisingly good). Ironic that Timothy Hutton starred in both movies.