I have a relative this happened to. She and her husband own a cabin cleaning business, and were cleaning cabins one day. She stepped into what she thought was a room. It was very dark so she could not see what she was stepping into. She fell down the stairs and has been hospitalized for over a year now. I think she can speak, but she can move arms a little bit, she cannot walk. All she did was open a door and walk in. Scary.