Please, what do you think is wrong with my cat?

She went from 9.2 lbs to 7.5lbs, yet eats extremely well. She was brought to vet, they checked a thyroid level which is normal. Today I came home from a trip and was told that the cat was at the vet. She was unresponsive and cold. They are keeping her at the very least overnight, running blood work, warming her, and giving her iv fluids. She is 8 year old indoor cat, but they tested her for leukemia and feline hiv anyway which are negative. I was thinking maybe diabetes. Does anyone have any other thoughts on what it can be. I am so heartsick over this. Please keep Sadie in your prayers.