I know its not rams (and by the way, Im so sorry to hear of your sad loss), but when my baby billy goat Toby was castrated by the same method, he took ages and ages for him to come round from the knock out drops the vet gave him. I have to say though, that both the boys were given antibiotics AND painkillers at the same time so that they didnt have too much discomfort afterwards. Once round (after me crying my eyes out with relief!) both boys were absolutely fine, no bleeding at all. I never want to witness the proceedure again though, the noise alone made me feel quite sick. Im glad that my hubby kept his distance, he would have been in a terrible state!
I dont know much about sheep, but could he perhaps have had a weak heart or something like that? Once again, so sorry for your loss.
Mary.