Not being able to jump up and run to the bathroom.
A lot of my classes run for 2 or 3 hours with breaks every hour. I never used to think twice about hopping up and just popping down the hall to the washroom. Now I sit there wondering:
If I get out of my seat now, how long will it take until I can straighten my hips and stand upright without holding onto something for support?
Is everybody going to see me waddling around like a demented penguin?
Will I be able to walk quickly enough to get back before class starts up again?
Then I either decide that yes, dammit, I WILL go to the bathroom, and then I get up and pretend to fuss around with something in my backpack until I'm reasonably sure I can stand straight and move without my right leg giving out. Or, I just decide it's not going to happen this time, and I spend the rest of class really regretting the enormous mug of tea I polished off in the first half hour.