My boy's at the vet now. His bladder was completely empty, so now he gets to spend the day there until it fills ack up again so that they can test his urine. He was NOT a happy cat when I took him... and right before I picked him up to put in the carrier, he was happily curled up with Allen in the bedroom

I'm so nervous. The vet did say he's gained a TON of weight since she saw him last. What could cause the big jump in weight? He's always been my thin boy.