Sudden Weight Loss Causes More Condition_symptoms What Would Cause Sudden Weight Loss In My Cat?

What would cause sudden weight loss in my cat? - sudden weight loss causes more condition_symptoms

My cat is 5 It has always been a big cat. (Weighing 20 pounds) We have noted the weight he lost the last two weeks. He eats and drinks well, always so active, as it seems ill. What is fever?