A cat vomiting old cat food may be caused by accidentally eating too much and suffering from indigestion; or the cat food may have deteriorated and tasted, causing the cat to be unable to eat it and vomit it out; or a cat may experience loss of appetite, lack of energy, or loss of energy after vomiting cat food. If the cat is unwilling to move, it may be that the cat is feeling unwell. The owner should observe it carefully, or send it to the doctor if it is serious. It may also be that the cat has changed to new cat food and is still not used to it, so it vomits it out.