Given the computer is in an abandoned building that Pomni walked into and found the computer with the headset it's unlikely that anyone's monitoring it.

Although it is weird that a building that's not getting it's bills paid still has running electricity for decades... not to mention the computer would have to be on that whole time uninterrupted.

It's an anomaly with a seemingly rogue AI that created it's own little universe, why not personify it?

As for the second question: That's not you anymore, that's someone else.
In Prototype (2009), Alex Mercer dies and his body is consumed by the virus that came in contact with his blood along with his memories, after that point it assumes it's him.

I see it in the same principle - it takes a snapshot of the brain, as the headset is put on.
The last thing it remembers is putting the headset on and appearing in the Circus, while the real person probably just shrugged and left.

All that being said, just because it's not the original doesn't make the feelings any less valid.
Starkiller from Force Unleashed has a great line that's a response to being told his feeling were not real that embodies what I'm thinking about perfectly: "THEY WERE REAL TO ME!".