One time, I was playing fetch with my dog in the upstairs hallway. I would throw the toy over the balcony to the downstairs, and she'd go run to retrieve it and then run back. We were having fun and all was good, but then on the final throw, I "hid" by the balcony and the door to my sister's room.
My dog came back and found me, dropped the toy, and immediately started growling. I moved closer to see what was wrong but she didn't respond, her eyes were fixed behind me. I looked back and there was nothing there, just the white door and white walls. Then I looked into my dog's eyes and I could see myself and the hallway reflected back, and behind me in the reflection was the dark figure of a person, it looked like a woman. We were completely alone up there, my sister and brother were chatting in the kitchen. I nope'd the fuck out of there and spent the next few hours downstairs.