Who decapitates a fish? Just a quick whack to the head right above the brain is a lot quicker and easier. And NO, DO NOT FREEZE him while he's alive. That's just stupid.
But like has been said, you can probably bring him back. You just need to start doing 80% water changes daily (twice daily if you can). Start BIG FREQUENT water changes, and see if you can bring him back. He's probably just sulking because he feels bad (oscars do that).
Anyway, HITH is on YOU, the owner. You failed at your responsibility as a pet owner to provide adequate conditions for your pet. HITH is completely preventable if you have good water conditions. In my opinion, you're lazy, and I don't feel bad for you at all.