Not sick at all. The only way it wouldn't die is if you don't smack it hard enough. How do you think I kill my fish when I go fishing. I smash them on the head with a mallet.
If you think suffocating them is more humane than instantaneous death by blunt force, be my guest.
As owners of animals that kill(via suffocation and crushing) and eat other animals in nature I would think that most of us would be ok with making such a small sacrifice and save it the gruesome and not so slow death of being killed by a constricting snake.