Originally Posted by DaneMcCloud
What does he see? Well, he sees his life in "The Sideways" flash, which I believe really isn't a Sideways flash but something else. His entire experience, which to him felt like quite a long time, lasted only seconds.
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.