Hope everything is okay, though you may be worrying too much. But I know how it feels.
Our ct was ill last week. For a period of about 4 days, she just didn't want to move. Even though she didn't look ill, she just hid away and didn't get up from her hiding spot for days. My dad was really worried and took her to the vet, but the vet said there was nothing physically wrong with her. The probable cause: the last thing my mum saw her eat was a WHOLE BIRD, beak, feathers, feet and everthing. Cookie was probably just feeling really shitty while the beak and claws and feathers digested.
As soon as she felt better, she went out and left a disembowelled mouse on the patio for us.
Such a lovely cat.