Other possibility that I am throwing out there...
Could he have that much of a physical reaction to our new rescue Lucie?
He really doesn't like her.
I put Lucie in a closed room for a week so Diablo and Bosco would smell her and get accustomed. They were fine. But Lucie is a very intense kitten when she plays and kind of scared Diablo out of his fur a couple of times, so he doesn't want anything to do with her anymore.
Anyone knows if depression is common in cats?