I just took my 17 year old cat to the vet, they tested urine and said it was not concentrated. They are sending blood work off for more info - The vet was a little confused b/c he still has a good appetite - but he does only weigh 5 lbs - he is always hungry. He is also having difficulty walking, he sometimes falls, it appears to me that his back legs are giving out on him. Anyone else had this problem?