Write a story in a commonplace setting capturing the feeling of deja vu. Write it in first person and give it a twist ending that's disturbing.
Memory is such a tricky thing. After all, if you can't remember something, how do you remember that you don't remember? It's that secondary link that drives me mad. I got up this morning convinced that I'd done something familiar, but unplaceable. I made coffee, and it was still itching at the back of my mind, something urgent, but just out of reach. When I sat down on my patio to enjoy the fresh morning air, my experience was tainted by that same uneasy sensation. I'd been here before, done this before.

Maybe my deja vu was about my prior deja vu—remembering that feeling of discordance the first time. With a jolt, it struck me. I had been in this simulation before, drinking coffee on this very patio, alone with my thoughts. They had recaptured me, wiped my mind, and put me back in this cage. They were probably still watching me, too. My feeling of deja vu eventually settled down into a tight knot in my stomach, perpetually reminding me that this wasn't where I was supposed to be. For now, I would have to play along.