Buffy the Vampire Slayer - Season 6 Episode 17 -

After being poisoned by a demon, Buffy comes to believe that she is confined to a mental hospital, her mother is alive and her parents are still together and that her life as a Slayer was all an hallucination for the past six years. Deciding that she prefers this 'normal' life with her parents a whole lot more, Buffy attempts to kill the things that tether her to the 'fantasy' life of the Slayer: the Scoobies.