Y.,
First, I'd have him checked over. He might be feeling poorly. Dogs mask pain VERY well... he could have a toothache, or something of the sort...
Then, if the Vet says it's behavioral, I would definately put him throught the program Kimmy suggested... "Nothin In Life is Free".
This program is all about's establishing the correct hierarchy(sp) within the house. If the problem is just that he's gotten too big for his little Chi britches, NILF will do the trick. I've "adjusted" several HUGE attitudes on dogs large and small with the program, from Poms to German Shepards. Otherwise, they would have been bound for a much different life, or no life at all (literally).
1. For a while, do not let him on the furniture or bed. put him a towel or blanket on the floor at your feet. The Alpha dog sleeps/rests at the top of the pile. Even very young puppies do this. The alpha puppy will almost always be at the top of a pile of sleeping puppies. So, his place is on the floor. We *do* allow our dogs in our lap on the couch to cuddle; and you will too again eventually. But, for now he belongs beneath, you both literally and figuratively.
2. Do not feed him your food. He eats only dog food: in his bowl, AFTER you eat the good stuff in front of him. The Alpha dog eats first, and eats the best parts. Everyone else gets what's left...Dry dogfood is good enough for a peon.
3. Crate him. By giving him crate sessions you are establishing your alpha-ness, and giving him quiet time. You are telling him he is not at the station in life that he belongs on the bed.
4. The message is "This is MY house. You live here because I allow you to. I can decide if you live or die, and frankly, I'm still deciding". Walk tall, speak firmly, and leave no room for question.
Good luck.
T.