Sorry for your loss.
Aflatoxins perhaps? Too many feed stores I know don't appear to know molds are life threatening... Either they don't know or don't care.
Best wishes.
Best bet for now is to let him sit somewhere quiet and safe with food and water within reach and his legs in a correct position beneath him... Probably. There's a chance it's a serious break. Can't tell without looking at him first hand, generally.
Best wishes.
Can he move his legs or do they dangle uselessly when you hold him? It's quite possibly a damaged spine or pelvic area. In which case chances are with enough time lying still he will heal.
Best wishes.