I can't name drugs, my my experience has been that the animal is given a sedative shot, and then remained with me until they fall into a very deep sleep (and usually longer, for me this is when I say goodby and often that takes me a while.) Then the second injection is given which actually euthanizes the animal. For small animals, this is best done directly in the heart, so once I've said had enough time, that injection is given in the back room (largely because it is upsetting to the parents--the animal at that point isn't feeling anything.)
Maybe I've been lucky, but I've been present for the euthanasia of several dogs, and several guinea pigs, and it's always been a very peaceful experience. None of the animals have appeared frightened or in pain.
I'm so sorry that your experience was upsetting--the decision to let them go is hard enough. I would ask your vet what they did, and why and go from there.