Examine eyes; look for 3rd eyelid extension. Look for watering, eyes
kept closed, etc. Check nose, ears, backside. Use a good light.

You are looking for signs of obvious illness, infection, lesions.
Anything out of the ordinary. Check his mouth and throat with a
flashlight, and if possible, help. Perhaps he has a lesion in his mouth
or throat, causing the hairball reflex sound.

Can you take his temperature? Yes, it has to be done rectally; Vaseline,
about 1 inch insertion. Normal temp is 101.5F Plus or minus about a
degree. It tends to be lower in the morning, or when they wake up from
sleeping. Over 102.5 is cause for some concern. Over 103.5 And there is
almost certainly an infection, somewhere.

You need to keep him hydrated. Will he drink the water pressed from a
can of tuna? I certainly home so.

If not, do you have a syringe, small baster, large dropper, or some
other device you could introduce small amounts of water into the side of
his mouth?  With luck, he will reflexively swallow it.

Keep him inside and quiet. Try to tempt him with any of his favorite
treats; preferably that are high in water content.

Beyond that, keep an eye on him, and monitor his condition.

Good luck with your little guy.

Usually, with a urinary tract infection, the first clue is that a
normally well behaved cat goes outside the litter box, because his
bladder hurts. I had a female cat that happened to, decades back.

He may have a urinary blockage. Can you handle him enough to try to feel
for his bladder? It's basically the same place as your is.

If it feels hard, about the size of a plum, there is urine that he can't
eliminate.

This is VERY SERIOUS, as the urine backs up into his blood stream and is
very toxic. Death can be very swift.

I hope you have a Monday MORNING vet appointment.

He may be suffering from something minor, or it could be very serious
indeed. It's hard to know, from your descriptions.

I worked for a vet, many years ago. But I have forgotten much.

Often the vet would just FEEL a cat and would know what was wrong,
immediately.

I did not have that skill; certainly not to the vet's degree. My
background was small animal surgery, not veterinary medicine. I parted
company over a long running dispute over declawing of cats. I don't
approve of it. It was a big money maker for the vet. I left.

I do hope your cat is going to be OK! I have just one cat, 12 1/2 years
old now, and she is very, very precious to me. I live alone, so she is
my only company.

I do know how worrying it is when your cat gets sick.

I do hope that whatever is wrong isn't too expensive. I know how that
is, too.

I always recommend rather than putting it on a very expensive credit
card, work out terms with the vet. Most are very understanding. As long
as they get their fee, eventually, most are OK with that. And most won't
charge you 22% interest!