Not sure if this has been posted before but it's a good interview with Nolan where he talks in some depth about Insomnia...
http://www.guardian.co.uk/film/2002/aug/27/features
http://www.guardian.co.uk/film/2002/aug/27/features
I wanted to make a film where night and day started to become confused. As you follow this character his perceptual distortion is increased, and you start to wonder whether you're seeing the whole picture and how much time has passed. So I wanted the audience to be floating a little bit by the end of the film.