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I am sorry to hear you are worried about your cat. My name is Rebecca. I am a veterinarian and will do my best to help.
Since I can't see and examine him, a little more information will help me. Is he eating and drinking? If you look at his gums, are they pink in color or do they seem pale?
Any vomiting or diarrhea?
Can you take his temperature with a thermometer?
The swelling you are seeing could be from an infection. Or, he could be "stocking up", retaining fluid, from a variety of things: liver disease, kidney disease, circulatory problems, heart disease.
If I could, I would check his gum color, take his temp, feel his pulses, listen to his heart, palpate his lymph nodes and internal organs. A thorough physical examination would be the place I would begin to figure out what is wrong.
If his gums are pink and he is eating normally, that is a good sign. If he has a fever, he may need antibiotics for an infection.
Let me know what other questions you have.
No, red gums would be gingivitis, and this would not normally cause the swelling you describe. I am glad to hear he is eating.
Can you post a picture of the swelling?
I agree he should see a vet in the morning; that would be best.
Let me know if I can answer any more questions, and how he is doing.
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