Ahh I'm sorry to hear about your cat, I know how you feel.
It's been six months since we lost our dog (and a year before that, we lost her sister!
). She had an illness where the vet said as long as we kept giving her this medication, she would be just fine... four days later, we lost her. The disease had complicated her heart. We were told, by another vet we had been going to, that her kidneys were starting to decline (her sister died of kidney failure), so we had her on a special diet, turns out that whole time she had this disease, where if the vet had just did the test... we would have had her on that medication the whole time, and her heart would not have been complicated, and we would still have her.