I was out sick a few days last week (you may have noticed a fever-induced tinge to my ramblings) and was reassured today (back at work) to find out that others had been ill last week as well. Being sick when all around you are well raises the question of what, exactly, is wrong with you, but if others have it then it’s whatever’s going around and probably nothing serious.

OTOH, I can’t really imagine how reassuring “Oh, it’s just something that’s going around” was circa 1350.