This happened to my VERY healthy happy cat a few years back.
He went out in the morning and barely crawled back that afternoon.
Seemed not to be in any discomfort though in fact, he was purring.
Took him to the vets the next day....and he could not find a single thing wrong with him. Threw out a few scenarios like, might've been bitten by a snake.....tick...etc. but no spine trauma at all.

It was very emotional for I couldn't possibly think about putting this otherwise happy healthy 2 year old cat to sleep...so we took him home and realized (as the vet told us...) he won't be able to go to the bathroom and will end up with toxic poisoning.


So, we had no choice but to bring him back several days later....and let him cross-over.

It's very heartbreaking and I am sorry you're going through this.

'Helpless' is probably the best word to describe what you're feeling right now!

I am so very sorry
!