It seems in chapter three of Kurt Vonnegut's
Slaughterhouse Five that Billy uses Tralfamadore as a means of escaping his Monotonous life and his past war experiences. Vonnegut published the novel in 1969, before post-traumatic stress disorder had entered our language (1980's), but Billy Pilgrim clearly exhibits symptoms of this disorder, one cause being how horrendous his war experiences were.
In the first three chapters, as Vonnegut jumps to and fro with the plot of the book, we still see bits and pieces of Billy's life during WWII. First, Pilgrim is stuck behind enemy lines after the Battle of the Bulge, barely surviving as a fellow american soldier, Roland Weary, continues to beat and intimidate Pilgrim as Weary sees him as a burden to him and the two scouts Roland has believed he has befriended. After the scouts leave Roland and Billy, Weary immediately attacks Billy, believing it was his fault. "It was entirely Billy's fault that this fighting organization no longer existed, Weary felt, and Billy was going to pay" (Vonnegut page 51). Pilgrim and Weary are then caught by the Germans and put into a POW camp as he is forced to reenact his capture, and is crammed into a box car with other American prisoners of war and watches a body of a fellow soldier is taken away from one of the cars.
It's not surprising that Pilgrim is having the flashbacks to the war as if he was really there or that he suffers from hallucinations either, but there is one question: Why the Tralfamadorians? Well, there could be multiple answers to this, and maybe they have more than one purpose. But I suppose that the reason Billy Pilgrim uses these aliens "shaped like plumber's friends" (toilet plungers) is that he has a lot of messed up and horrific things in his memory which seem stuck there. And obviously, toilet plungers are in the business of unclogging drains, and Pilgrim seems to use the Tralfamadorians as a way to "unclog" these bad experiences in his life despite not actually saying it in the text. But like I said, could the Tralfamadorians be used by Vonnegut to represent something else? and if so, what would they represent?
PTSD information from
The National Institute of Mental Health and
The U.S. department of Health research portfolio online reporting tools