[user104658]

You can only hang upside down for so long before you die. Blood pools in the head for one (can cause brain haemorrhage), and for another, the heart isn't designed to pump blood that way round the body so blood pressure rises and the heart can simply fail. Like it's totally safe to be upside down for a few minutes, probably even a few hours, but 12 hours + and things can start to get bad.

I read a story a whole back about a caver who got stuck upside down and eventually died. They managed to get people in beneath him and could talk to him, he was talking at first, eventually passed out, and had died before they managed to free him.