Somtimes this just happens, Im not an expert as you know but sometimes nothing works and the life slips away, we had one lamb from a set of twins it stopped breathing 3 times in 4 minutes, we would swing it, rub it, thena few minutes later it had stopped !!! so we repeated and started breathing, this happened 3 times, it did have alot of gunk coming up from the lungs, maybe it was that blocking the airway? hard to say, we were v lucky that time but sometimes we are not so lucky, dont beat your self up !!