He seems to be a lot worse today, he hasn't been the same since he had the anesthetic (which i've since learned wasn't necessary). He's not eating or drinking at all aside from what he's having through a syringe. His head is constantly down and it seems to be an effort to pick it up

. Could this be from the anesthetic that he had yesterday afternoon?
Did the vet give metaclopromide after the anaesthetic? An anaesthetic slows the system down, and can play hell with the guts. A gut stimulant medication is very useful for limiting this.
Also, he's going to need syringe feeding (and fluiding), floppy and refusing can be system slow down (metaclop needed at the minimum, and maybe a steroid jab too), weakness through not eating, dehydration, and even "just" a pain reaction depending on what's going on.
If the deterioration has been more noticeable post anaesthetic then I think you can definitely point the finger in that direction. And yes, anaesthetic shouldn't be necessary, but if the only way you can get necessary treatment from a vet is to let them use gas, then it has to be done. I hate it, but I feel short of taking over the surgery at gunpoint and forcing them to do things the right way sometimes you just have to take the risk.
I'd suggest 0.5ml Metatone (available at chemists, and some supermarket pharmacy departments) and as much food/ water as you can syringe into him. Either ground down pellets or off the shelf powders such as Critical Care will do, right now you need to be giving him nutrition and trying to provoke his guts into working again. If you can get a vet, then a metaclopromide injection is something I would very much push for.
Floppy head is never good, but I have managed to get one or two through it (also had more than one or two not come through it). Most notable was Piggedy, who was floppy, not moving, not chewing when things were put in her mouth. Cracked out my whole kit that night, and put her back in the cage expecting the worst. Next morning she was in the back corner of the cage, I assumed she'd crawled there and given up. Reached in prepared for the worst... And she bit me and ran off to the hay!