My pony was sedated in a veterinary hospital for a castration, and he has never been the same since, the change was apparent as soon as I got him home, and he has never improved. I have some experience of sedative and anaesthetic drugs effects in humans, and its effects are a bit like alcohol, different cocktails can cause different reactions, sedation is tricky because some people can be aware, I am a fighter if not fully under.
What annoyed me is when I tried to discuss it with the vet, basically, it was highly unlikely, and they couldn't tell me what they had given him and how much. If I had him sedated at home, you get an itemised bill, and I could have seen the effect myself. Now unless it was something like major surgery I would never let be admitted even as a day case.
Accidents happen, I know a horse that broke its leg in 12x16 stable overnight, it managed to get up and was stood at the stable door in the morning, and for complex surgery they need to give them a GA or heavy sedation, but I do not think the side effects are often fully discussed.
I just hope it was quick for the horse, and they still had an IV line in.