They're very good at hiding sickness, I think. I lost my Junebug in February under similar circumstances. She was getting up in years, was diabetic, but still lively and doing okay, and then over the course of a few days just stopped eating, went downhill fast, and was unresponsive one morning. The vet said there was nothing they could do but just end her suffering. Right before the end she kinda woke up a little and I got to kiss her goodbye.
So sorry for you.
Cover your knees up if you're gonna be walkin' around everywhere.