I lost a cat a few months ago because a few warning signs, I thought were from the cat being crazy. She was always a skinny minnie cat would would sometimes run from/attack ghosts and do other lunatic things, so it just didn't occur to me there was something really wrong. She was the barf cat I wrote about above.
So she got a blood clot and was in terrible pain and half paralyzed and had to be put down. A few times earlier, she had done this thing where she couldn't walk and looked like she was in pain, but then quickly got over it. I think I've posted about this before. Still sad to think about. For real:

If I would have taken her to the vet the first time, it's a relatively easy thing to fix or prevent from reoccurring. Saddle thrombosis. It actually kills a lot of cats.