I expect stats to drop a bit during the christmas/new year week and I don't get a huge amount of traffic, but my Jetpack stats dropped off precipitously on December 10th. Traffic is about 10% of what it was for the preceding month, and less than 10% of the previous few years. And, it's all very suddenly.
Google analytics does show a more expected level of traffic, so it seems like it's got to be the plugin or the theme (Atahualpa)... both of which were updated on the 9th...
http://www.sustainablepractice.org/ is the URL