I've been a bum this week, too! I only ran one day, rode my road bike one day, and mtn biked 2 days. Sad, but true. I'm like you- I need a "mental" break from training every now and then or I just wear out.
We'll get back on the wagon tomorrow- no worries! For now, enjoy the day off and relax (and probably eat a little more than normal- what the heck- Christmas only comes once a year).