A modern rehash of René Descartes's "I think therefore I am" problem. He asked, essentially, am I living a fantasy dreamed up for me by a "great deceiver".
Replace "great deceiver" with "computer simulation" and the argument plays out the same way (albeit, with more probability in the modern case)<p>Ultimately, your existence is exactly what you perceive it to be. Speculating on the nature of our existence, on this level, is indicative of those who don't have to pay their own rent :-) You can chase your own tail on this one literally forever. As we cannot access the simulation we are running in (just as you can't really think about thinking) this idea becomes a debate on par with the existence of God. It cannot be proven one way or another.<p>All this aside, I'll admit it was a fun read.