While anxiety may account for your symptoms, there are other possibilities which need to be ruled out. You need a full medical work up,
Cat Health Monitoringby
The problem is cats can not tell the owner when it became ill. New owners know for some time after the cat showed behavioral changes such as more frequent sleep, not eat or diarrhea...
LIVER DISEASE IN DOGS AND CATSby
Helpful Buckeye has received several e-mails asking about liver disease in dogs and cats... for as evidence that the liver is involved in what your dog or cat is experiencing. That will be followed...
Cats hiss because when they’re frightened/stressed and there can be both medical and behavioral... normally, no vomiting or diarrhea, runny eyes or nose , or any other symptoms that would suggest a medical problem...