You have changed your routine and redecorated the house (and possibly moved furniture around to compensate). You may be caught up in the Happy Holiday Spirit that makes everyone smile or you may be a big grouch who doesn't want to talk to any of those Happy Holiday-ers. Believe it or not, most of you don't go around your house the same way throughout the rest of the year (smiling, singing and/or humming) ... well, some may go around grumping, but that's not what I'm getting at here.
The point is that your dog is probably pretty stressed out. You may have people come over for the holidays and you need to understand that your dog may not be able to deal with the people, excitement and hustle-bustle of this time. During these times, watch your dog.
If he or she looks like he's uncomfortable with a person or situation, than why wouldn't you give your dog a little quiet time in a bedroom or in his crate? Take some time to do a little Internet searching and learn how to read the body language of a dog; this is a good article from Modern Dog. Keep in mind that each and every dog is different and will display different language and these are only basic guidelines. There are actually hundreds of different signs of stress, but these are the most common.
Take some time to get to know your own dog and his or her signs so you know what things you need to work on. You will end up with a better rounded, happier dog.
I am sure I don't need to tell you how many dog euthanasia's I used to see working at the veterinary clinic during December. Most of them were in because the dog had bitten a relative and the owners couldn't deal with it.