After reading this book, it seems to me like Vonnegut is portraying Billy the Pilgrim as having some form of PTSD. Also because of the book's confusing mannerisms and style of writing, it could even be construed that Vonnegut has PTSD and is trying to soothe his symptoms by writing about them. These symptoms are understandable regarding the situation. Not only are Billy and Vonnegut involved in the war in a combat sense, they have also experienced the Dresden bombings. These reactions to the bombings are interesting as both Billy and Vonnegut are part of the Allied Forces and should not have been directly affected by the bombings as they were not the targets.
I think Billy has developed PTSD before the war has even finished. He is already having flashbacks and has eccentric mannerisms that include being visited by Tralfamadorians. Although I can't regard him as insane (yet), his actions thus far seem to fall in line with the symptoms of PTSD. I don't really know where I'm going with this but Billy's mannerisms are definitely not just because he might be a little kooky or "out-there". There is something else going on in Billy's (or Vonnegut's) mind that is making him act this way. What are your thoughts?