I absolutely love my job and the people who I work with, but I have to say that going back to work after the Xmas break is very difficult. To me, at the end of every work year, it's like you've ascended a huge mountain and you're standing on top of it triumphant. Then, when you return from the Xmas break for the new year, it's like some bugger has put you back down at the bottom of the mountain...and you have to climb it again.
My only advice is never return from holidays on a Monday, but rather go back later in the week - it always seems to soften the blow. Either way, it's pretty traumatic getting back into a rountine.