Originally Posted by CosmicPal
I agree that his "sideways flash" may not have been a 'sideways flash" after all.
None of the others are aware of their sideways flash. Only Desmond gets to see his "what-if" life, or "past" life, or whatever it is.
I think Widmore is up to something. I think he's showing Desmond what could have been or what a wonderful world he can experience if he follows through on Widmore's orders on the island. So, he didn't experience an actual sideways flash like the others have.
That "perfect" world that Desmond entered will also provide the answers to all of his questions, resolve all conflicts, and provide him with sublime, everlasting love. Hence why he came to with a profound smile on his face and was more than willing to help out Widmore.
I don't see it that way.
Desmond has been the only person in the series so far that's been able to pull together multiple realities.
Unlike the other rescued Losties, he chose NOT to come back to the Island (Jack, Sun, Hurley, Sayid & Kate) on his own. In this episode, he's been drugged and taken back to the Island.
What he sees after the electromagnetic pulse on the island shows him is life post 1977 nuclear explosion. Somehow, he realizes that reality is wrong and is willing to help out Widmore any way he can to make sure "The Sideways" doesn't become the one true reality.
As I stated earlier, I think he saw something that wasn't shown on-screen, which particularly motivated him to help Widmore.