Not the worst nightmare but unsettling nonetheless. I was in an elevator and had the task of visiting floors 2, 0 and 4. The floor counter first showed 2. I wanted to go to 0 next but it displayed 4 instead. I looked away for a short while and when I looked back, I was already on floor 56. "Must be a damn tall building," I thought, without any idea where I was in the first place. Again, looking away for some time, looking back. 2706!! This floor number made me paranoid. After each glance at the floor counter, I felt the sensation of free falling, and the higher I got, the stronger the sensation. So when I got to 2706 and started to free fall, my brain basically pressed ESC and "quit the game". Sometimes it happens, when I feel physically uncomfortable inside a dream (itching, pain, falling etc.), I escape and exit. I woke up and this wasn't part of the dream but I imagined being in a bizarre elevator, going down to floor 0 and encountering a vast darkness as the doors open. Just cold and empty darkness, and if you stepped into it and turned around, the elevator would be gone. Then I fell asleep again and was in a town, the same one that the elevator was in (although there were no windows in the lift, there was a similar tone or presence). It was a desolate place, grey and empty. I ran across something resembling a town square, and someone shot at my direction. I hid somewhere and that was it.