Sort of a balance drill...
We do something interesting in my class. We lift one foot to about mid-shin level. Next we start tipping our heads back until we're looking at the ceiling, some folks lose their balance here...but most don't. Finally, we close our eyes. Our teacher points out that our suddenly losing our balance is "100% mental" and we're supposed to imagine the last thing we were focused on. "Nothing has changed, the ceiling IS STILL THERE. Why are you falling? Your perspective has changed, but it's something you CAN control.", he says.
-Radhnoti