cat question

My cat has been hiding under the hutch and won't come out. He just suddenly decided to become anti-social. He must be coming out during the night to eat and use his litter box but other than that we never see him. He has not acted like this since the time we had another cat. We only have a dog, but they have always gotten along. I'm really confused why he's a acting this way..any advice or suggestions would be greatly appreciated. Thank you.