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eroock
Since: Sep, 2012
Scorpion451
(Edited uphill both ways)

This happens all the time in sci-fi and fantasy shows, so I'm certain there's a trope, but I can't find it.
The episode usually begins with the hero waking up in an insane asylum. They ask where they are, and the doctor or nurse says something like, "Oh, you've had another episode! You've been imagining a whole other life. But you're not really a superhero / star ship captain / chosen one, are you?"
Examples include the Star Trek TNG episode "The Inner Light;" Buffy, "Normal Again;" Ash Vs Evil Dead, "Season 2, Episode 7." it's common in TV, but it's even the clinic level of Alan Wake.