Total Recall is like this too.
It could all be real.
Or, once Quaid sits in the chair and goes to sleep, the rest of the movie is in his mind and the fade to white with the twilight zone music at the end is him waking up.
Once I caught on to that after seeing the film as an adult it's hard to watch it straight. It just seems obvious, especially since everything the guy said would happen does--part of the adventure is believing that it's all real in the moment and not just a fantasy.