Good news, Hermes is fine and home after an overnight stay at the Vet.
Since he's been given a clean bill of health urine-wise, they say it's behavioral.
While I don't want him to be sick, it would have been much easier to deal with if it was medical - you treat the problem, the other one goes away. If it's behavioral/mental, it means understanding your cat, which is no small feat (seriously, if I could understand cats I'd be rich). So it'll take more training, caring and study to figure out what caused the incident in the first place.
In the meanwhile, I've changed my linens and kept him out of the room when I'm not there. When I am in the room, I bring him and and try to keep the room feeling positive so that he sees the bed as a sleeping/playing/resting place and not a bathroom. I'm also making sure his litterbox is spotless and praise him when he does use it.
The vet also recommended
Feliway - a plug in that uses cat cheek pheromones and is supposed to give off a calming vibe. It's a better option than drugging - especially since Hermes is not manic, depressed or otherwise suffering from emotional issues - but it isn't fail-proof and comes with a hefty $50 cost for a one month's supply. I read a lot of reviews and the bag was so mixed that I'm holding out a bit before going that route.
But for now, the most important part is that my little one is home and mostly happy.