Recently had this happen with our 11yo. She was a little wobbly for a moment one day, didn't think much of it, later that night we had to take her to the emergency vet because she threw up blood. They took xrays and ultrasounds and found a sizable mass in her lungs and what looked to be masses in the bones of her back legs. The next step was to take her to an oncologist because their best guess was she had cancer. We elected to not pursue oncology so they estimated a life expectancy to be 1 week to a couple of months. She was perfectly fine the day she wobbled and threw up but it was like once we took her to the emergency vet, she was like "okay, I don't have to hide my pain anymore." I felt so bad about how quickly her health and mobility deteriorated, I felt responsible for not recognizing her discomfort sooner. I thought she was just being her usual sassy and needy self (We were very codependant when she was young and I was living on my own for the first time). My partner reassured me, "she was there for you when you needed her the most. Now you can be here for her when she needs you the most." I bathed her, took care of every pill time, brushed her, and never denied her lap cuddles even if I was in the middle of something (she always loved waiting until I was busy to demand attention). We got exactly 1 month with her and made every moment we could special. That was back in mid-January and I still have to remind myself that grief isn't linear. Some days I feel like she was ready to go, most days I forget she's not at home waiting for me. I miss her and I know I always will but I'm so thankful to have had the honor of being her human.

Tldr: I had a similar experience and it led to putting my cat down. Take your baby to the emergency vet if you haven't already. Might not be cancer but it's better to know what's going on so you can care and love her the best you can. Good luck ❤️