I am sorry your kitty is having trouble. Such a drastic change in behavior can in fact indicate that something is wrong. Your kitty may have injured himself somehow, and may be uncomfortable, or he may have an illness that is making him feel funny. There is a very long list of things that can be wrong, and it is impossible to tell you what they may be based on his symptoms. At the top of the list would be a urinary blockage, which is a life threatening condition and requires immediate medical attention if your kitty is to survive. If he cannot pass any urine he needs to be seen by the nearest emergency vet right away. Please consider rushing him in to be seen and let me know if I can be of further assistance. If this has been helpful, please hit the green accept button. Good luck!