sick cat 10 years old

Question
Yesterday my cat suddenly got sick and spent the whole day under the sewing machine, coming out only twice to have water and use the litter box.  She is an indoor cat and we live in a senior complex.  She had only eaten Friskies Poultry Platter but during the last year they quit making it.  They suggested Purina chicken for seniors which she liked but they also quit that. I tried a multitude of other cat foods.  she doesn't like a mixture..Only chicken.  Purina then had me try Purina One chicken for senior cats and she's been eating that for 2 weeks.  She's always been very playful, until yesterday.  She threw up twice yesterday and today she is back to sleeping under the sewing machine cabinet and not eating .  What could be her problem and how can I help?  

Answer
I would recommend a trip to the vet for an examination and possible blood tests.  She may have a fever that is causing her to be lethargic and hiding.  Or there could be something more serious such as kidney or liver disease that is making her sick.