10 Stargate SG-1 Fates Worse Than Death

Although widely regarded as one of SG-1's comedic highlights, the fourth season episode 'Window of Opportunity' could quite easily be seen as complete nightmare fuel were it not for the framing with which it is shown.

During a routine mission to observe a geomagnetic storm above a world housing Ancient technology,, alien archeologist Malachi starts operating the Ancient device and initiates a time loop, using the Stargate to envelop 13 separate worlds in the same 10 hours until the loop can be broken.

Standing alongside Malachi at the altar are Col. O'Neill and Teal'c, who are both aware of the loop and must find a way to stop it. The pair must spend every loop repeatedly convincing others of their plight, whilst also learning the language of the Ancients piece by piece (with an occasional cycle here and there to goof off and learn juggling/play golf through the wormhole)

Although the team eventually manage to break the loop, they are contacted by the Tok'ra, who inform them Earth has been unreachable for three months. Given each loop is approximately ten hours, this means O'Neill and Teal'c went through at least 216 loops. Had they been unable to stop Malachi, there's no telling how long this could have gone on. With O'Neill's sanity already beginning to fray within these first 200, eternity would have truly broken him.