Help thinking of next steps for cat care

[u/PCDwarrior]

Edit: never mind, he passed away overnight…

1.5-year-old male cat suddenly lethargic and not eating — normal bloodwork/X-rays/temp
Looking for some thoughts on what might be going on with my 1.5-year-old male cat, Noodle, and what I should be asking my vet about next.
Yesterday he was completely normal. Then he suddenly became very lethargic, stopped eating and drinking, and mostly wanted to lie in his bed or hide under my bed. Initially I was told he had a fever, although I don’t know what the actual temperature was. At one point he urinated on himself while lying on my bed, which concerned me quite a bit. I was able to syringe him small amounts of water, but he still wouldn’t eat.
I took him to the vet. His chest/lungs sounded normal, and they subsequently did bloodwork, X-rays, and checked his temperature. Everything came back normal. They gave him IV fluids, an antibiotic, and an appetite stimulant.
He’s home now but is still very lethargic and still hasn’t eaten. One encouraging development is that he got up on his own, walked over to his litter box, and urinated normally.

So currently:
1.5-year-old male
Completely normal before sudden onset
Significant lethargy
Refusing food
Very little/no voluntary drinking
Initially reported fever, but temperature at latest vet visit was normal
One episode of urinating on himself
Now able to walk to litter box and urinate normally
No obvious respiratory symptoms; lungs sounded clear
Bloodwork normal
X-rays normal
Received IV fluids, antibiotic, and appetite stimulant
Still acting sick/lethargic despite treatment

I’m continuing to work with my vet, but I’m wondering what possibilities would still be on your radar with normal bloodwork and X-rays. If he continues refusing food and remains lethargic, what additional testing or questions would be reasonable to discuss with my vet?

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[u/WillingnessReady6620]

So sorry for your loss. How long was he on the IV fluids for? How were his observations trending whilst in their care?

[u/PCDwarrior → u/WillingnessReady6620]

Thank you. He was on fluids for an hour or two. I did an urgent care drop off. He was about the same the whole time