Christmas Blues

I think this happens pretty much every year. The after-Christmas morning blues. I'm not sure exactly what causes it, but my theories are as follows:

1. The unwrapping experience is never quite as exiting or fulfilling as you hoped.
2. Having time to myself to chill and just hang out is unusual for me, and I sometimes don't know what to do with the time. Usually, I do chores or try to get stuff done, but I don't want to go that route on Christmas day.
   
3. I have heard athletes experience a bout of depression after finishing with a significant goal, such as winning a championship or the Olympics. Similarly, after all of the effort, time, and stress put into the specific goal (Christmas preparation), maybe I'm lacking direction momentarily after my previous goal was actually accomplished.
4. Except for going to stores for gifts and groceries, we've been cooped up in our house for a couple of days. Getting out to do something (besides just a walk) sounds like it would be nice.

My visiting relatives seem to be a little on the downward side emotionally too, but they are also away from home and perhaps getting sick of being a guest in someone else's house. So does anyone/everyone else experience this, or is it just me and/or my household?