Wildman had some health issues and needed a few vet visits to work out what was going on. We finally decided it was a recurrence of his upper respiratory infection.
He has a chronic sinusitis from when he got sick as a tiny foster kitten. I had to do many desperate measures to keep him alive (2 of his litter mates died). So now he has a condition that flares up occasionally.
We did 2 rounds of antibiotics to try to clear it up. He has the was I call the "snotty nose syndrome". When cats get blocked noses they stop eating and drinking.
So he got dehydrated and was running a temperature of 104 oF. I gave him subcutaneous fluids and helped him eat some wet food. It took a few weeks but now he seems in fine fettle.
Hope he keeps up the fine fettle. Too stressful otherwise!