You step through the open door and your foot fails to catch the floor, and as you crumple, with a  yelp, into a long dark fall, you try to readjust and reconstruct, erasing your old expectations and addressing this new reality, and your back twists round and you compensate, raising your right knee to your chest and twisting your neck up and left, further than it wants to go, and it clicks unpleasantly, and you try to remember to breathe in. And as you stabilise, still tumbling down the unlit, wallless chute, you realise that that probably was not the door to the lavatory.