I have 6 cories (mixed species, but school together) that share my planted 36-gallon hex tank with a small school of white skirt tetras. This morning, my pair of albino corys was doing their up-and down the tank walls 'mating dance' that they always do before eggs show up in there... Anyway, the male got a little bit crazier than usual, even; splashing around at the surface like crazy and putting on a show. It was really entertaining to me until my most assertive tetra (affectionately called the 'jerk-fish' around here) got annoyed by the little cat's antics, darted across the tank and hit him -hard.
The cory immediately flipped onto his back and floated to the bottom, where he lay upside down!

I thought he was dead for a minute, i didnt even see breathing. Once i did, i went to get my net to nudge him back onto his belly, but by the time i got back, he had righted himself and swam away. He hid in a corner for awhile. I examined him pretty closely at that point and found no outward signs of injury. Now hes back to the 'mating dance' and acting normally, so i guess he's fine???
I know certain species of shark will faint in response to stress, but ive kept Corydoras for a decade and have never seen or heard of them doing this. Has anyone else experienced this? If so, was the fish ok afterward? It was pretty crazy to witness!