I'm so glad you had your cat spayed!! Please, don't fret.
First of all, the shots alone usually make your cat sleepy and out of it for a day or so.
On top of that, she's out of it from the surgery and the anaesthetic.
Cindy's (kat18e) advice is perfect, although she probably won't feel like eating real soon. Even if the Vet gave her food, she probably wouldn't have eaten it so soon after surgery. Keep an eye on her - if she doesn't start eating and drinking within 24 hours, then call the Vet.
And don't worry about the disolving stitches - again, just keep an eye on them.
Hubby and I work with feral (wild) cats, and we always have them receive all their shots, de-worming medication and get spayed or neutered at the same time. It is a lot of stress for a cat - getting shots, getting poison (that's what de-worming medication is), and being subject to surgery. But they're amazing creatures, and we haven't had a problem yet! They are out of it for a day or two - and the ferals get released back into the outdoors! Though we usually leave the males at the Vet's for a day longer than we would if they were coming home, and the females often stay for several days after the surgery before we release them back into the wild.
But we use dissolving stitches because we can't be sure we'll be able to trap the cats again to have the stitches removed. Knock wood - we've never had a problem.
So your inside kitty should be just fine! She might want to be left alone - just respect her wishes. If she wants love and scritches, give her lots!
She's going through the same thing as if you were given heavy medication, had surgery, and then were brought home. You'd need a day or two to recuperate, too.
...but if you see anything of concern, feel free to post. Or call the Vet. Or do both.
Many of us are crazy about cats here (
), and we totally understand your worry! We go through it each time someone gets a cat spayed or neutered. We're here to hold your hand through it, too.
You're just being a good kitty-mum.