Our 7-year-old tabby started moving sluggishly Thursday and slept on my lap all evening, then slept all day yesterday, and then was out on the porch this morning with really rapid, shallow breathing. Took her to the vet, who said her lungs were filling with fluid, basically feline congestive heart failure. Probably started to be serious a few weeks ago, but cats simply don't exhibit symptoms until it's pretty much too late. There were things we could have done to keep her going for a couple of weeks or maybe a month or two, but there was no reversing the real problem, and treatment was going to be expensive. For the last 35+ years our household has always had at least one cat in it, so it's not like we haven't been through it before, but damn it's hard to look into those trusting eyes while the shot is being administered.
At least she went out with an Astros' win.