In the Buffy episode 'Normal Again' the possibility is raised that Buffy is actually a patient in a mental asylum and that everything in the Buffyverse/Angelverse is simply her delusion, starting when she 'meets' Merrick in the Buffy movie and ending when she regains her sanity once more after 7 years at the end of the final Buffy episode 'Chosen'. This Angel episode is perhaps the most convincing of many arguments against the theory, things happen in the Buffyverse which Buffy never knows about which would be impossible if it was all just in Buffy's head where events could only be seen from her point of view.