The act of falling asleep abruptly (crashing) on the day of Christmas, usually in the evening. This may be due to a variety of reasons, namely: over eating at the family dinner, drinking excessive amounts of alcohol, exhaustion from dealing with family, staying up late on Christmas Eve and waking up early on Christmas (excitement), or just to buy yourself some me time away from the family. The Christmas Crash usually occurs between 8 and 12 hours after waking up on Christmas morning. The slumber may carry over into the night's sleep, causing you to have a disturbed sleeping schedule for a few days.
I think I suffered the Christmas Crash last Christmas...there are pictures of me sleeping on the couch with my stocking in hand while everyone else enjoyed their Christmas.