I was just wondering if anyone had any advice, our lovely 18 year old cat, William, has become suddenly lethargic and weak overnight and seems 'different'. He is an indoor cat (by choice for the last 4 months) he just no longer wants to goes outside and enjoys being lazy and pampered inside, so I know he has not ingested anything unusual.
Although he is 18 he has ALWAYS had a healthy appetite, he is up and active miaowing for his breakfast from around 6:30 am everyday and fussing for treats all day long. He also likes playing, laser pointer and with his mouse toys, for short periods of time. He normally eats three sachets of Felix Senior a day and sometimes a few munchies, he drinks plenty of water. He has never been ill, only vets visits have been for accidents due to fighting with other cats back in his outdoor days

However this morning when I went into his bedroom he was curled up silent and just looked at me, no jumping off the bed miowing, no fussing for food, I tried him with a few different flavours of food but he just looked away. He had been to the toilet in the night and his poo looked normal, I lifted him off the bed and he urinated in his litter tray, again a normal amount, no straining, no blood. He has not vomited. His heart rate and breathing seemed as normal, although for the last few years he has sometimes seemed a bit 'wheezy'. Its hard to explain but he was just not himself at all, so weak, just wanting to sleep and not wanting food- so completely out of character. I know he is an old cat but he really never acts like this at all!

I think we should take him to the vets today as it is such a dramatic change, my partner thinks he might just have a cold or be a bit under the weather and we should just watch and wait.
I was just wondering if any other catchat users have any advice on this? Or experience with their cats becoming suddenly lethargic.
Thank you. X