I was hoping to receive a reply from you with some additional information about Sheamus, but I will send you an answer now, and if you have any further questions, just click 'reply' and I will be happy to continue our conversation.
If you brought him to the vet, I'm assuming he was examined thoroughly, perhaps imaging was done of his jaw and swollen area of his face and he was diagnosed and treated. If the vet had no diagnosis for you, your description of your kitty's symptoms could have various causes. He might have a dental problem, like an abscessed tooth or infected gums, causing the swelling in his facial area. He could have injured his jaw when falling from a height, unbeknownst to you, and have a hairline fracture or more serious fracture. He could be experiencing an allergic reaction to something he ate or something he contacted inside or outside the house, if he goes outside.
He's weak because he probably can't eat, and I'll assume the vet gave him some fluids if he was found to be dehydrated, and also, may have given him some I.V. nutrition. If he's still at the vet for treatment and observation, if he has any type of infection, he's probably also on I.V. antibiotics.
I hope your furry boy is feeling better, soon and please let me know how he's coming along. Thanks!
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