About two months ago one of our cats named Smoke started losing weight and became very lethargic. When it became extreme, we took him to the vet two weeks ago where he was diagnosed with feline diabetes. The vet prescribed twice daily insulin shots of a particular type of human insulin in a very, very tiny dose. The vet said that just a few years ago the diabetes would have been quickly fatal but this treatment is relatively new. The dose is delivered by a standard diabetic insulin injection pen using a rather long but impossibly tiny needle for the tiny dose. I can't even feel the needle entering the skin which is worrisome. One piece of good news is that our cat doesn't even feel the injection and just enjoys the extra attention while purring away. The other piece of good news coming from a veterinary website is that if the diabetes is caught early, a majority of cats in a study went into remission after only four weeks of injections.
If any my friends in this forum who have older cats with these symptoms, don't hesitate to get the cat to the vet and don't lose hope.
As an aside, as expensive as insulin is these days, the dose for a cat is so small that the injection pen holds as many as 300 (!!!) doses so the cost is manageable.