Since yesterday, Jack just hasn't been himself. He's still affectionate and purrs. But has no energy. What is really making me worry is that he growls, hisses and bites when he is picked up. Normally, he may or may not let you hold him but never ever growled at his Mom and Dad. I'm definately going to take him to the vet first thing on Monday. Could he have a stomach problem or what? I'm at a loss for what could be wrong.