Is Buster depressed?

My cat Buster was diagnosed with FIV last year and for about a month now he has been losing wieght very quickly and doesnt seem to do much but sleep. Normally he has quite a bit of a temper but his mood has remained calm since around the time of his initail weight loss. All of this is actually making me depressed. I know that it is normal for cats with FIV to lose wieght quickly but Buster just seems so down. Perhaps his time is coming, but he really hasn't shown any signs of real sickness. So I guess what I would like to know from all of you is if you have had a similar experience, maybe, or have you heard of cats getting depresed? Thank you for your concern.

Is he eating? Drinking? Does he seek out attention from you at all?
Has he had a checkup lately?

I wouldn't give up on him yet. Take him to the vet and let them do bloodwork on him. There could be a medical cause for his symptoms. How old is Buster?

I am praying for sweet Buster! keep your spirits up! I pray alll will be ok.