The 10th Floor Loop

I am a senior hotel cleaner. The hotel I work at is very strange: it does not have a 13th floor (due to superstition), every floor has identical decor, and there is a huge full-length mirror at the end of every corridor. One late night, I was cleaning the corridor on the 10th floor when the elevator suddenly broke down. I then realized I had dropped my walkie-talkie in one of the guest rooms I had just finished cleaning. I decided to go down via the stairs. I started walking down from the 10th floor, and every time I passed a floor, I habitually glanced at the floor sign on the fire door. "9, 8, 7..." When I reached the floor marked "1", I pushed the door open, only to find myself back in the 10th floor corridor. I thought I had taken a wrong turn, so I quickened my pace and ran down again. "9, 8, 7...2, 1" I pushed the door open, and I was still on the 10th floor. I desperately tried countless times, until I accidentally glanced at the huge full-length mirror at the end of the corridor. I let out a shrill scream, because I finally understood: I will never get out of here. What happened?