There was that one movie that came out in '94 called
BRAINSCAN starring Edward Furlong (John Connor of T2).
It was about a horror movie loving teenager who is desensitize to violence.
After playing a computer game which he ordered people in his town begin to
die. And he starts to remember killing them. Throughout the movie he is
not sure what is real and what is not.
Also, a different Star Trek Next Gen episode:
This one also with Riker, He is sent down with an away team to survey a
planet. The entire team injestes some kind of gas. They have to beam them
all out of there. When Riker revives he learns that it is now 30 years
later and that he is suffering some kind of memory loss.
Anyway, he relizes that it is not real and then thrown into another
"reality" as well. (I don't remember the name of this episode, maybe
somebody else can help out).
Screen-L is sponsored by the Telecommunication & Film Dept., the
University of Alabama.