I'll add to that - if you're in a waiting room in the oncology unit, and there's not enough seating - stand up if you're one of the healthy people there (!!!!!)
I think the same rule applies to antenatal clinics ... if you aren't pregnant, don't continue to occupy a chair while the pregnant women in the room have to stand (or sit on the floor). Sometimes those waits are two hours. It is a long time to stand up when you are pregnant!