A plastic container 1 inch wide and 4 inches long fell into my upstairs toilet as it was flushing. The toilet still flushes. Should I be concerned? Will it affect my toilet down stairs?

Will it affect my toilet down stairs?

It could, you will just have to wait and see. It may pass to the street or it may get stuck in a turn somewhere and cause tissue and solids to accumulate. If that happens at least you will know why, and it is an easy fix.

Let's check and see. Take as big wad of TP and flush it down, Did your toilet start to back up? If no then do it again. If yes then try hooking it with a closet auger If that don't get it the toilet will have to be pulled and gone in from the bottom. Good luck, Tom