my cat is very ill~~prayers please *UPDATE*

One of my cats is VERY, very sick. We're not sure what is wrong with him. We found him, and have always thought he was old, so he might just be aging. He doesn't take care of himself anymore, he's had an upset stomach since yesterday, and now suddenly he can't pick his head up. He's lost a lot of weight. I'm taking him to the vet tomorrow, but I really don't have a good feeling. I think they are going to tell me that something is wrong that can't be fixed, tell me to put him to sleep, or tell me that he doesn't have very long left.

They can't MAKE me put my cat to sleep though right? I won't put this cat to sleep. He's the biggest, most bad @$$ cat ever, and I know if he could talk he'd say he just wants to go naturally.

Please send some prayers for my Gus.

UPDATE: Thank you all so much for your prayers. Gus was very sick through the night and barely moved at all. I rushed him to the vet, and they said that he is old- over 10. I found him a couple of years ago, so even though I suspected he was old, I never knew for sure. They said he probably has a hyperthyroid, which they can put him on meds for. I'm just waiting for the results of the bloodwork. It seems that the worst possible case scenario is NOT happening. Thank you all again so much.