This happened about 6 years ago in my previous house. I was laying in bed looking out into the upstairs hallway as my door was open and my bed faced the door. I could see all of the hallway and the full length mirror hanging opposite the stairs by a piece of string running along the top of it.
Randomly the top of the mirror came off the wall while the bottom was still in position. The mirror then fell forward, the bottom having never touched the floor. Because it fell forward, it slid all the way down the stairs smashing at the bottom. My mum then screamed at me and my sisters for throwing the mirror!
Now what I find weird is that the string should of snapped and so the mirror would of somewhat slid down the wall, the bottom of the mirror hitting the floor and then would fall forward! It was like it was pulled off the wall top first. I didn't find it freaky because it was just so strange.
After that any mirror or picture hung on that wall would fall off! My parents of course still didn't believe what I saw!