I'm sorry to hear of this with Bertie. It's important to note that any cat - particularly a 15 year old who has much less reserve than a younger cat - who has been anorexic for 5 days is now profoundly dehydrated and electrolyte imbalanced. Cats don't know how to drink enough to keep themselves hydrated. Bertie needs the attention of his vet at your earliest convenience. 15 year olds who become anorexic for this length of time usually are in renal or hepatic failure or an age-related malignancy is present. His ataxia ("drunken sailor" can represent profound weakness (such as might be seen with anemia), toxicity associated with renal or hepatic failure, or either encephalopathy (brain disorder) or myelopathy (spinal cord disorder).
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