I'm inferring that you have a sleep apnea problem which has only partially abated through surgery. I'm sure the neighbors are not pounding on the floor for their own amusement or to inflict misery on you. The problem, apparently, is that you snore very loudly. There's no simple solution. Obviously you're trying the surgical route. But the fact remains that you snore so loudly that it's keeping your upstairs neighbors awake. I would suggest moving to a home where your bedroom shares no walls with neighbors.
I know that's not a comforting suggestion. But you are in a difficult position. It's unreasonable to ask neighbors to put up with extremely loud snoring from a neighbor's apartment. You are not the only person who has had this problem. A woman was cited into court in Davis for just this reason. See link below:
P.S. You shouldn't take what I wrote above as legal advice, as I don't practice law in California. It's just my perspective on the facts you present, in light of general principles of law. If you need legal advice, please consult a lawyer who holds California licensure.