I've fiddled with the idea of writing a story (not sure about the length) from the viewpoint of a mentally insane protagonist. However, because of the mental condition, I'm thinking it would be harder(er) to introduce background information. Unlike 3rd person, where I could drop in what he is feeling (memories, etc.) I don't have the experience with 1st person to know about special techniques for doing so. Any good ways to bring in relevent background information when the character is not a reliable narrator of events?