Check his thyroid!
Hello. I'm not a vet. I'm a nurse. But I wanted to share with you what I have learned. Same symptoms with my cat. Had a senior profile done. He has hyperthyroid. There is a thyroid blood test to confirm. I'm not saying your cat has this, just have him checked. My cat was sluggish, stopped eating, coughed when he purrs, lost his voice. Started him on methimazole and his thyroid decreased, he stopped coughing, started eating, got his voice back after 3 weeks b/c the size of his thyroid shrunk. My vets and specialist started with the diagnosis of hypertrophic cardiomyopathy and kidney disease, but these are both caused by the hyperthyroidism first so if you catch the elevated level soon enough, the medicine for it works perfectly.. A cat is considered a senior at age 10. Yours is almost 10. It could be the start. Most senior cat's get hyperthyroidism. The good thing is they respond so well to the medicine that they will return to their former self, unless it wasn't treated in time. Like mine still has cardiomyopathy and the kidney disease is a little worse b/c the decrease in blood flow to the kidneys, but what was really getting him down was the symptoms from the hyperthyroidism. The not eating, lethargy, and malaise is his creatinine going up some but he bounces right back after subq fluids. I would just have his thyroid checked. And then keep everything I've told you in mind. Good luck! Christi