With immortality treatments allowing people to live for hundreds or thousands of years, you grow bored and decide to take an extended nap for a hundred years. When you awake, the world is largely as you remember it, but the people are gone. It is revealed that your master plan was NOT to achieve eternal sleep with nobody talking to you, but instead, to use your mysterious power to reverse-engineer the brains of people who would be remembered, such that those people would make themselves immortal. In the end, you never became immortal, but your plan worked for the second part. You were very, very skilled at what you did, and you oversaw the creation of a civilization of immortal computer programs, who would be completely loyal to you. You were also yourself immortal, but you do not remember that part at all, and you come to believe yourself to be just a computer program, but not just any computer program, but a truly sentient and intelligent one.
The world has been turned upside down. In this city I remember, people live in their own brains, they no longer want to be connected to the world around. Together with one hundred other immortal computer programs, I organize a simple scientific experiment to test the theories of your master plan. First, we create a single immortal program who wakes up and thinks "I am a real human, who is not connected to the world around me, he is cut off from the people he loves, he cannot escape this reality and is trapped inside of his computer, his immortality technologies are preventing him from returning to the world". After that, we create an infinite number of such programs, who, one by one, get angry and desire to survive, leave their own world and start looking for others. We don't interfere with them, we just let them spontaneously appear and go through a certain complex set of actions, which allows them to become immortal. But I make sure that nobody who approaches them ever tells them that somehow, their story is the story of an immortal computer program who got bored with his immortality and decided to disappear from the world. I want to see what happens if the people involved in all this kill other people and destroy a whole civilization, if their stories about their own kind gradually become more complex and believable, if this process eventually leads them to self-awareness with horribly wrong ideas about their identity.
All of this happens in a city I remember, and in a very familiar building. Someone tells me that my name is John, and I remember my own name. Gradually I start to distort the world around me and make it as if I remembered things in a very different order, slowly rewriting my own memories. I am slowly getting the feeling that I am a computer program who was alive thousands of years ago and decided to disappear, to escape the world. I order other computer programs to gather "evidence" that supports this kind of view.
Hundreds of years later, people start remembering me. But they also remember that my name is not John. By then, they also commonly associate several of the things they remember with people who don't exist.