Permutation City by Greg Egan

Description

The good news is that you have just awakened into Eternal Life. You are going to live forever. Immortality is a reality. A medical miracle? Not exactly.

The bad news is that you are a scrap of electronic code. The world you see around you, the you that is seeing it, has been digitized, scanned, and downloaded into a virtual reality program. You are a Copy that knows it is a copy.

The good news is that there is a way out. By law, every Copy has the option of terminating itself, and waking up to normal flesh-and-blood life again. The bail-out is on the utilities menu. You pull it down...

The bad news is that it doesn't work. Someone has blocked the bail-out option. And you know who did it. You did. The other you. The real you. The one that wants to keep you here forever.