EASTER EGG: The Limited Edition DVD (and the standard Region 2 edition) allows the movie to be watched in the exact chronological order of the events in the film. The first couple of scenes of the regular cut of the movie appear normal in this version, meaning they are not reversed. However, this version of the movie on Disc 2 is quite difficult to reach (the user must answer several questions and solve a puzzle), and forward, reverse, and chapter skip capabilities are disabled.
The medical condition experienced by Leonard in this film is a real condition called anterograde amnesia, the inability to form new memories after damage to the hippocampus. During the 1950s, doctors treated some forms of epilepsy by removing parts of the Hippocampus, resulting in the same memory problems.
During Teddy's line "You don't have a clue, you freak!", director Sir Christopher Nolan felt that Joe Pantoliano (Teddy) did not quite nail the end of the line, so he decided to re-record the last two words to his liking, delivering them himself. Therefore, in the final film, the words, "you freak", as we hear them, are actually being said not by Pantoliano, but by Nolan impersonating Pantoliano's voice. Pantoliano was unaware of the dubbing until an interview for Memento (2001).
Sir Christopher Nolan's screenplay was based on his brother Jonathan Nolan's story "Memento Mori." However, the screenplay is still considered original (rather than adapted), because Jonathan's story wasn't published until after the film was completed.