In my Grade 7 piano exam I went to turn the page in my B piece and the music fell off the stand and landed in a heap on the floor. I swore quite loudly, then panicked and just turned to the examiner looking like a deer in headlights. She said "it's alright, just pick it up and carry on." which I did and got a pass level mark for that piece (and the exam overall) so she clearly didn't hold it against me, thank goodness! In my defence that piano had seen better days, still serviceable musically but a bit battered and the music stand was extremely wobbly. In my Grade 4 viola exam I was so nervous that at the end of the first piece I dropped my bow. It finished on a very long note and my hand was shaking, I went to lift it off the strings and it just fell out of my hand. Thankfully it was still in one piece, the accompanist and I had a little chuckle about it and all was well.