Apocalypse stories are tricky because you need to think of something so large, that it's a threat to the population of whatever planet the story's taking place on; but not large enough so everyone dies. If that happened, well, we wouldn't be alive to tell our tale, no?
You want an Apocalypse/Post-Apocalyptic tale, but we need to think of a why first. Why is our society/planet/galaxy crumbling?
Unfortunately, past, present, or future, there's not much types of apocalypse we can choose from.
Past - A disease no doctor can cure overcomes the world and the human race seems to be breathing it's last breath. WWII in a nutshell
Present - Nuclear war or the story of 1984.
Future - The story of Terminator or the story of Wall E, pick your poison. Turns out Global Warming did exist and now the Earth is as good as Europa. Brave New World
In all three time periods - Aliens, Zombies, Meteor round 2, Super volcano eruption, Earthquake measuring +10 on the Richter scale, Super Tsunami, Super Hurricane (essentially, the Big Red Spot on Jupiter, or it could be a hurricane that traps us in a building and stir-craze happens causing us to kill each other)
What's funny about Apocalypse is that it means "any universal or widespread destruction or disaster." That could just mean society, so say society, as we know it, suddenly changes. Like, a new leader takes charge and the way we function changes greatly because of this. Our halcyon days are over, essentially.