Okay, sorry I meant to update last night but it was a rough one for the both of us. My stomach was in such a state that I almost fainted at the vets office.
The x-ray came back normal, and I'm still waiting for the total bloodwork to come back, the vet noticed immediately that his red blood cell count was pretty low. He gave me some meds for that, and some anti-inflammitory meds but he is starting to think he may just be a little anemic. Still waiting for the blood results to come back from the lab though. Fatso is doing a lot better this morning, still drained of energy but he got up when I woke up and did the kitty rub on my legs. And he went back to his kitty bed and went back to sleep, but he is making a little progress. He's back to eating his hard food and using his litter box normal again.
This vet is amazing, he made sure to explain every little detail and gave me advice for what I should do. Plus he said I can bring Fatso back within 48 hours for a free re-check. I'll only be charged if he has to run more tests, but for a wellness check he said it's free. SO then I got a little nervous thinking "how much is this costing me that I get a free follow up?" but it was only 200 euro, roughly $260 (give or take) and I got 2 xrays, the health check, blood work, and his meds. Not to mention the cell phone number for the vet in case anything new comes up, or if I have any questions at all.
Thanks guys for all the good thoughts, and nice comments. He is my big hansome kitty and I'm glad he's doing better. Slightly, but definetly better

I think any progress is good progress.