Mmm, Christmas brings its joy as well as its burdens. A few weeks of revelry with reduced exercise could result in a larger waist circumference than you expected.
Don't be overly critical of yourself, after all if you maintain your rituals, but maybe with a few classes missed, then your post Christmas workouts should not be too hard. Maybe a few classes where you try extra hard, push that intensity up another notch and drive out the Christmas cheer then you will be back, fit, lean and looking gorgeous for the rest of the holidays.
Remember, the energy you put in must be used, or stored: if it is stored then you have to work to get it off. Alcohol adds to your energy intake, one beer is approximately 130cals (Australian standard drink = alcohol calories, 70 + carbohydrate calories, 60ish), just consider that when you open the second six-pack.... it'll make your six pack disappear almost overnight: and you won't get it back so quick either!
Have fun over the holidays, but not so much that you undo all of your hardwork put in over the year.