When I was younger, I went to a school named Trowbridge in the Bayview area of Milwaukee. It was built in 1894 and added to in 1905.
Anywho... I believe I was in 3rd grade, my last year there. In 4th and 5th grade, I went to a different school to finish elementary. Some of us would stay after school for playground activities. I was going inside for the bathroom, as I had just gotten to the two sets of doors and reached out for the handle. WHAM! The door (the heavy-duty metal doors) I attempted to grab swung open so fast. I had no time to react. I was on my back when I realized what had happened. I didn't see it coming, and I definitely didn't see who slammed it open. Nobody saw what happened. It happened inside this smaller entryway.
I was probably lying there for a good minute before the playground attendant arrived. I was able to get up and walk. And my twin brother helped me get home. We lived pretty close to the school, about a block away. When I did get home, my mom figured I was concussed and had a lovely-looking hematoma above my brow, so off to the doc I went. Everything was ok.
Those things in your home are self-transporting and when they see a chance, they relocate to the most dangerous place for you. Another version of trees jumping in front of cars.