She is not involved in sports, or has had trauma to either knee, but for no reason at all they will just collapse under her, causing her to fall down. It used to only be her left knee, but tonight it was her right knee that collapsed. These attacks are becoming more frequent-the most recent was this evening(right knee) on Friday it was her left knee. Afterwards her knee is warm and swollen.
WHat is going on? She gets very upset when it happens.