Many years ago, I agreed to care for my downstairs neighbors' dog while they were away for a few days, and they neglected to tell me that the dog was epileptic or to give me its medication. So I was rather concerned when the dog stiffened up and fell over, though it recovered a few minutes later. I mentioned it when the owner returned, and she said, oh, yeah, it had a seizure? Happens alt the time, nothing to worry about. (Thanks for letting me know...)
Yeah, that would have been a helpful tidbit! :-P This dog keeled over on the sidewalk, stiffened a little, and then pooped while laying down. But it was starting to perk up after several minutes. Poor doggie (and owner).
Sounds exactly like what my neighbor's dog did.