I can imagine a wheelie chair under a window totally catching people out :OD
The number of times I have placed my foot on to a 'climbing aid' that moves is numerous. Only yesterday I hauled my arse out of a pub window on to what looked like a filing cabinet, resting on a very uneven surface.
Woah.... woahhhh... woaohhhhhh.., is the usual outcome, with my outstretched arms desperately trying to keep upright. I'm sure the bastards do it on purpose
I have done that before ion the office and not even doing a bit of illicit derping! That feeling as the thing you are standing on starts to shift. Yeek!
I haven't fallen yet, touch wood. Got stuck on a fence yesterday that tore into my back.., all for a bus depot!
Oucha. Hopefully your shoulder means that the universe owes you some injury free time!