This has happened to me a few years ago. I was working in a scare attraction in The Netherlands. This required working in the dark for days in a row and not seeing any daylight in the winter periods. Many people say this is the explanation of my experience, together with the sounds and music that surrounded us. But I know what I felt and this was real.
That day I was doing a show about ghosts and every actor in that company has a problem with that room - for I am not the only one who has had an unexplainable experience there. I was doing my show and during a pure technical part I could get out of sight. I had to open another door for the visitors to enter after the technical show. So I put my hand around the door and waited for a lot of noise from the show, so I could open the door without being noticed. After waiting a while I felt someone stroking my hand and whispering "Hey, psst..." As a shocked reaction I pulled my hand back. I opened the door a little and looked into the next room, surrounded by mirrors. I expected to see a colleague, but the room was totally empty. My heart was racing and I opened the door entirely, so the light of that room came into the show. I didn't want to be in the dark anymore. The visitors entered the room, although I didn't leave them in there for very long, as I had the strong feeling we weren't alone. After that show I never felt completely relaxed in that room anymore.
The strange thing is that all the actors have different experiences. Some of them see someone walk through an alley which cannot be there (because of the angle of the mirrors). Others see someone lying in a shattered mirror. Others see "The Ring"-like people passing by for just a short moment.
Now we are all thinking it is a friendly ghost who loves what we do - scaring people. However, that makes it probably fun for him/her to play with us in the same way. And with that thought in mind I feel quite safe.