New here with a weird question.

My cat, Figaro, has feline cystitis and is on a special diet from now on. Science Diet C/D. He nearly died last year. He is 9 years old now.

ANYWAY...I've had this feeling that something is wrong for the past few days, only he doesn't seem to be in any pain or discomfort in the least. He is not lethargic or unhappy like he was when he was sick before...quite the opposite. He doesn't want to be away from me. To the point of throwing himself against doors to be near me. He MUST sleep with me in the bed, and be carried around the house or he meows contantly. I don't know what this is all about. I have a vet appointment for 9am Friday, but I am really worried. What would cause an otherwise normal cat to become super clingy?
Nothing has changed at all in his life. Not even cat litter brands hah.

Any thoughts?

Are you sick yourself?
My cats act like that when I or someone else in the house is sick....even if they (the person) are not aware they are sick yet.

I'm not sure what it could be, but as long as he is eating and acting normal I wouldn't worry too much...The vet may be a good idea though

This is a rapid behavorial change so please do bring him into your vet asap. There could be many reasons for yoru cat acting this way.
Like stormy posted, with my cats when they become excessivly needy like that usually means they are seeking comfort because something out of the norm is upsetting them.
And the longer it goes on like that, the more they will start to act out, and the more problems will happen.

I wish you luck.

Have you changed anything recently..?
New job, gone different/longer hours, new furniture, moved furniture, new neighbor, stray animals around your home, new litter, etc....

Cat's do NOT show pain until it is almost to late. If you sense something is wrong- then GOOD for you, means you are in tune with Figaro, get him to the vet quickly- trust your gut instinct

Nothing has changed at all, there are stray cats, but just the ones that have ALWAYS been here. No furniture moving, change in hours, or litter. The soonest the vet can see him is first thing Friday, which is when he is going. I'm really stumped.