My cat did the same thing last year ... Once it got to the point of coughing every few hours - I called the vet. He ended up having pnemonia and was severely sick. Once he got on the meds - after 7 days he was fine. But he also got the pnemonia as a result of allergies. Your cat doesn't have to be outside to get allergies. Mine is indoor too and he has them. He also had to get a cortizone shot which really helped. I'd take him to the vet immediately ... A cat SHOULD NOT cough.
It is pointing out that the stomach of your cat is not working properly. So you must contact some veterinary doctor.
Well I am no expert but I think you should take her to the vet now before it gets any worse.
My cat is behaving the same way today, very strange the lack of energy and occasional plaintive cries. I've an appointment booked for the vet tomorrow and will give his answer here afterwards.