I thought I was leaning through the curtain onto a solid wall. I was actually leaning through a curtain onto… nothingness.
The moral of the story? If you’re ever onstage and want to briefly lean on the wall behind you, you’d better be damn sure that the curtain is actually flat up against that wall like you THINK it is (and not, as in this case, a few feet away).
And, yes, it hurt.