Were you watching History Channel when you fell asleep? That used to happen to me sometimes; although they generally do more WWII stuff, or did before Aliens apparently built mankind.
Still, they did WWI stuff once in awhile. I've often fallen asleep and dreamed my dream was being narrated by Stephen Hawking while also dreaming I was there with the Manhattan Project team. Which is obviously absurd--I'd never actually do that sort of project.