This would make for a terrifying twist on a sci-fi movie -- they arrive back on Earth after being gone so long to find out that they forgot they had never left. Any movies like that? (Planet of the Apes seems close)
I won't spoil it, but if you think that concept is neat, you owe it to yourself to go watch _Moon_. It's one of the best sci-fi movies I've seen in a long time. Highly recommended.
Capricorn One doesn't have that twist, but it's about a fake Mars mission. I saw it when I was a kid and for some reason it made a big impact on me. (Reminder for myself: watch it again to see if it's any good).
Having also really liked it when younger, I watched it again relatively recently, and I thought it was terrible!
Stuff (music, art, films, books, whatever) that isn't very good can yet have a major impact on a person (usually a young person) if it presents, however badly, some idea they find compelling, but haven't seen portrayed before, so have nothing to compare the particular execution with.