Whew, this movie INTENSE. I will freely admit that I can't handle horror movies and such. Early in the movie they introduce Joe's wife. A crazy event happens and she is missing and presumed dead.
I think they do an incredible job in increasing the intensity of the "clues" and really get inside your head. Is he going crazy or is she trying to contact him? I don't think I should say anymore than that other than expect to be at the edge of your seat.