The difference between legitimate psychosis and the ability to speak to the residents of the afterlife is a notion that's certainly approached in many films, though few actually throw themselves behind it as the full narrative drive. For the new upcoming British film The Messenger, it looks like this is exactly where they're getting their fuel.
The film tells the story of Jack, a young man who has spent most of his life in some form of institutionalisation, subjected to every drug and every treatment the doctors can think of in an effort to treat his delusions. Only they aren't delusions... he really can see dead people. Jack then becomes embroiled in a murder investigation so that he can pass on a message from the victim to his wife. Jack's unusual and obsessive behaviour worry everyone, but most especially the police officer trying to solve the crime.
The Messenger certainly looks interesting, like it has captured something of an emotionally and psychologically frustrated tone, particularly in the lead performance. However, it does, from this trailer at least, come across as somewhat laboured, stern and worried people sitting in stark places making disconcerting declarations at one another. Of course, that's largely what trailers do and it's maybe just the tense tonal juxtapositions that make it seem more awkward. Still, looks interesting.