standing-"not sitting"

I have noticed for about a week now, my cat Gigi-7yrs. not sitting. She is eating standing up, when she is not she lays down. She is kind of lazy, but she used to at least sit up. I took her to the vet yesterday, and she was checked everywhere, even bum. She said there was nothing wrong with her. What I would like to know is why she is doing this now. Anyone have their cats do this?

How does she bathe or I mean, clean herself? She must sit to do that at least!
If she has no arthritis or is not overweight, perhaps Gigi just chooses not to sit when you are around?

did the vet take blood?? at 7 it is the perfect age to get a "senior" panel for later use or to catch organ issues early

She is on a diet, she is 16lbs, she semi sits to clean herself.
She always sat before, even to watch the birds outside.

No the vet didn't do a blood check. I have been going to her for over a year for weight issue. She still has to loose some, but lost two lbs over that time.

This may sound like I doubt your vet's checkup ,but what about her tail? Could she have injured it someway? I noticed the same "symptoms" you described going on with my Lil Bit and a week later discovered an abcess starting from an infected puncture wound. It was so small before it abcessed that it couldn't be seen. Maybe a possibility??

The vet checked her tail, and surely if it hurt her she would have been sensitive when touched all over. I will keep on checking myself. Thanks for your input.