In 2007, I was told I had a disease I had never heard of. It started with my knee popping out of place as I climbed on my bed. When I went to the hospital the following day, it snapped back into position as a doctor examined me.
I had another dislocation in the same place in 2009 as I bent down to pick up a bag. I had several other dislocations after which the leg would snap back into position.