I had a wonderful dog for 14 years, and he was very rarely sick. He tore both ACLs (I didn't even know dogs had knees, let alone that they had anterior crusciate ligaments, those things in knees that athletes are always tearing) when he was about eight. That affected his quality of life later, but he still lived to be 16 or 17 (he was a rescue so we're not sure of his age).
So why, when we are miserable with, say, the flu, do we say we are sick as a dog? I am pondering this because, like a sizable percentage of the US East Coast population, I have the flu. I'm quite miserable, actually. I ache all over like someone beat me, I have a headache, my throat hurts like heck, I cough all the time, and right now I can feel I'm spiking a fever.
But I did want to thank the folks who posted Amazon reviews of my books in the last couple of weeks. Almost every title got a new review, which is pretty good, considering that most of them have been out for well over a year. Of course, they weren't all glowing, but even a somewhat-negative review is better than no review. The exceptions were the fantasy novella Where Magic Rules, and the new novel The Nostalgia Gambit, but I have hopes TNG will get a review soon.
So thank you, and I'm going back to bed now, because I'm (you guessed it) sick as a dog.