I use a blue exercise ball instead of a desk chair. This allows me to bounce on it since I am prone to fidgeting.
Five minutes ago, I was preparing my expense reports from last month. I stood up to get a paper clip from my shelf. When I sat back down, at the moment where I should've contacted the ball, there was only air. There was a loud thud as my ass fell hard onto the carpeted floor.
I looked around me, and the ball had rolled to the far side of the cubicle. People ran over from two offices down to see what the source of the thud was.