Fics where the character wakes up in 'The Real World' and is told that their entire life was a coma dream or a delusion. More info at TV Tropes.
Death Note
** Wonderland by RobinRocks
T, Complete, L/Light,<5,000
- Light Yagami awoke to white walls. Screaming. Written for LxLight Club's Alternate Ending contest. Onesided LightxL.
Metal Gear Solid
Through a Glass, Darkly by Athena Crickey
K+, Complete, Snake/Otacon
- One man's reality is another man's dream. But Snake's never had time for pithy philosophising.