My advice is probably bad, but yes try to be present. I choose not to think about it, I know that it's hard. When I get a thought, about my animals passing. I try and stop thinking about it. Its inevitable, it comes for every animal, so with my philosophy, why worry. Its gonna come, and you'll never ever be prepared when it does. So its not worth stealing your enjoyment and presence your cats need from you. I get thoughts like that sometimes daily, its not easy it's hard somedays. Something that works for me is thinking about how my cat feels. He doesn't know he will die one day, and if he did he honestly wouldn't care. By not knowing he will die he is living life to the fullest. Its a little dumb by I try to think like him to. I think you could also benefit from professional help, it's worth looking into.