How the Flash Sideways Fits by sudsiestpanda

Hi, this is my first theory. Sorry if I've taken anyone else's from the past. I try to keep up and enjoy reading them, but there's so many that it gets hard to keep track.

Anyways,

I think the flash sideways is a longer version of Desmond's "time travel" during the episode "Flashes Before Your Eyes".

My evidence for it not being a real place is this:
Desmond seemed to just drop in after his exposure to Widmore's device, which happened later on the island than the bomb going off. If it were along a real timeline, wouldn't Desmond show up after everyone else?

Time doesn't seem too strict there, as evidenced by Sun and Locke arriving at the hospital at the same time.

There doesn't seem to be a clear origin point for it, i.e. it's hard to say "this world is simply a result of x not happening"

........................................
Now, here's my guess about how it originated:

When you're exposed to the light at the center of the island, you get sent to the sideways world. There you're able to create whatever world you think you deserve. However, whatever choices you make there will follow you whenever you decide to leave.

The first time we saw this was with Desmond. He turned the fail-safe and was exposed to a bit of the energy. His wish, obviously, was that he'd've proposed to Penny when he had the chance.

In retrospect it seems like he did have the chance; however Ms. Hawking talked him out of it and he would up back on the island, mostly the same but with the gift/curse of seeing bits of the future.

With Jacob's brother I think he wanted a lot, and he ended up with a lot while in his imaginary world. He was judgmental and very curious while on the island, so I imagine him in a world where he cast himself as a ruler, lording over people with an iron fist. In return, when he finally left that imaginary world (which took the blink of an eye in real time) he was cursed to become the smoke monster, a being who could scan people's deepest thoughts but could never leave the island and was forced to just sit in judgment of others for the rest of time.

So, finally, I think the incident at the end of Season 5 put everyone on the island into their own little connected dreamworld (as it may have exposed them to the core of the island because of their location). What we're seeing in the flash sideways is them getting a chance to shape the world they want, or maybe the world that they believe they deserve. It happens for mere instants in real time, but perhaps what they do during the sideways has either led them to be rewarded or punished by the island during this whole season.

Thanks for reading!
Erik