Hi, compared with most of the other replies I actually have actually had a similar experience to you. This happened just before and I was looking for answers when I came across your thread. It is night at the moment and my brother alerted me before as my two shaver chickens were making a racket in the back yard in their cage. I thought it might have been a cat as sometimes they go near the cage. But when I went out there I couldn't find anything. Instead I see one chicken (my favorite - which makes it worse) sitting on the ground looking very confused. I saw the other one near by but she was standing and looking more like she was checking if the other one was ok. I stuck the ok chicken back into the covered part of the cage. But my other one wouldn't move. I checked her for injuries but I could find any. So I left her for half an hour and came back to find her a little better - at least standing up. I couldn't think of any other reason for this to happen unless she was sleep walking or something and fell out of the covered part onto the ground - which is only about half a metre down. So I don't know - it could happen.