Friendly Cat Suddenly Aggressive??

Last night my poofy fatty cat who is usually the most laid back of the bunch (5 cats total) started growling and hissing at any of the other cats who came near her. She also would growl at me if I tried to pick her up, although she would let me pet her and wanted to come sit on my lap.

Assuming there must be something wrong to make such a huge switch (just that morning, she'd been sleeping in a pile with 2 of them) I took her to the vet this morning. They were unable to find anything wrong with her except a very low-grade fever (about 1 degree above normal). They gave her a cortisone shot for a flea allergy and in case she were in pain but basically said they couldn't find anything wrong.

She's a completely indoor kitty, spayed, and she's had all her shots. Does anyone have any experience with this kind of behavior change? She is kind of terrorizing the other cats because she'll flop down in the center of a path and snarl if anyone tries to go past her.

~Sapling

can it be possible that she is pregnant and you don't know it ???

If she's pregnant, I'm gonna sue the vet who spayed her.

lol..maybe its not that then..how long ago did u get her spayed

About 6 mos. She's a little over a year old.

These cats are all related too, so they grew up together. Stray momma cat, you know the drill...

well she just got her shots and maybe she is still sore then...give her time

Well, she didn't get a shot till I took her to the vet for the irritability.. she got her vaccinations at the same time she got fixed.