We have four cats ranging in age from 1 and a half to 16 years old. Two girls and two boys. About two days ago the 13 year male does not want to leave the bed room. Is not hiding. But stays on the bed. Normally he would spend some time on the bed but would also be in the living room and kitchen. He is eating and drinking. He will leave the bed room briefly to eat and drink then rushes back to the bedroom. His coat is shiny and he grooms himself. Appears healthy. I think something scared him or he got in an altercation with one of the other cats. Any ideas on this? Thanks.