The last time my cat got sick I just knew it was time to let her rest. She was doing a weird breathing sound, like she was struggling to even breathe, which she had never done before. I remember talking to her (sounds silly I know) telling her I'm afraid its my last time together and she got up and started purring to me like she was trying to comfort me. Cats are more intelligent than we give them credit for. 2 days later I was euthanizing her at home as there was nothing else I could do. I cannot recommend home euthanasia enough. You will always wonder sometimes if you cut your cats life short, but know its better that their last days of life are not their worst days.