The belief after watching a film that it could be real life. Most well known cases are the matrix (the belief that we are all in a game) and inception (the belief that we are all dreaming and everything is inside the mind of the person believing this). Most cases are harmless fun for kids but can lead to a warped perception of real life (people thinking inception is real have killed themselves in the belief that they will wake up afterwards in the real world)
Robs gone mad after watching inception. He keeps waking sleeping people up with a 'kick' to bring them back up one dream level & thinking he can act like an idiot cos hes dreaming!" "I know! Major case of filmception
When your watching a film of a film within a film and you dont know what layer of the film your in.
A good example of this would be Cloverfield or Suzhou River.
Where in the film you see the film from handheld camera's perspective in the film.
Guy 1: I can't tell if im in a film or not, so i chopped my hand to see if i had a robotic left arm.
Guy 2: I think your in a bad state of Filmception!