Not to contradict you, but
Mr. Tech Support, as in the spanish original version by Alejandro Amenabar “Abre Los Ojos”, plays a significant role in the story, telling David precisely what is really happening and when the dream started. I mean, that’s the apogee of the story, where it had to arrive.
I’ve often wondered this about the movie Croupier.
How do we know that the events of the movie “really” happened to Jack? Perhaps he just made it all up for his book.
I got a great uncertainty about threads like this:
(spoilers for Vanilla Sky, The Truman Show, The Game, and The Others)
What if I haven’t seen Vanilla Sky, or The Truman Show, or The Game, and I enter a thread named “Movies that ask what’s real and what’s fake” and the thread is full of spoiler boxes? Wouldn’t I suspect that everything is fake in those movies? Next when I see them, they’ll be spoiled for me? I think I’m suspicious enough, as well as any smart doper, to realize that even with spoiler boxes those movies are losing their sense of… surprise. That is, a surprise is a surprise when you don’t know there is something hidden. Even in The Others, which is very obvious what’s happening.
I don’t want to spoil the party, btw.
Nitpick about The Others:
Actually, the servants were already aware they were ghosts.
No problem Dex, I know you guys are busy. Thanks for the fix.
Soul Surviors (which I liked better than Vanilla Sky, but most people on imdb disagree apparently), Abandon, Urbania…
In Perfect Blue Mima has quite a few identity issues to work out, and starts blurring the movie she’s working on with reality, among other things…
dark city
A few more
The Other (the 1972 movie, not The Others)
Sleuth
Penn and Teller Get Killed
How about Spider
…where we are never REALLY sure if Ralph Fiennes is reliving his childhood or if all events just are part of his twisted imagination
About Minority Report, not only was it what you said but also
What about the whole ‘people who are put in stasis dream the rest of their lives away’ Theoretically anything that happened after Cruise’s character was captured and put into stasis could be just a dream. A dream he made up to be all nice and comfy in the confines of his own head and not feel there is unfinished business.
Love that movie. Have been a huge Madeleine Stowe fan ever since. And all of Rickman’s stuff is gold, as usual. Although honestly I wonder about the mental state of people who have actually seen it. I mean, I saw it, and I know my mental state. 
Staying on-topic, if you like Closet Land, check out Death and the Maiden for another reality-in-question movie.
Thought I’d also mention Naked Lunch, from William Burroughs’ novel. Incidentally,
Burroughs shooting his wife in the head playing “William Tell” – that actually happened.