I don't eat more at Christmas/New Year or eat when I'm not hungry it's just the types of food I have this time of year IYSWIM? I don't generally have butter, goose fat, wine with my roast dinner, buffet food (the staple of every Christmas party), Christmas pudding, etc and people don't tend to give us family-sized boxes of chocolates and biscuits except at Christmas. So for me it's type of food rather than quantity.
I've been on SW since August so my usual intake is lots of vegetables and fruit, pasta, lean meat, fish, etc with occasional treats. I knew it was going to be more difficult to keep going at Christmas so I maintained control by deciding in advance that I wouldn't deny myself but I would make good choices wherever possible (e.g., nice Christmas satsuma instead of lebkuchen) and be self-limiting with not-so-good choices (e.g., having one biscuit and enjoying it instead of half a pack) and for all the rest simply accept that it is once a year and the important thing is to get back on the plan afterwards.
If it's constant and the weight gain is the start of more weight gain then that's when it's a problem. If it's Christmas weight that will gradually shift when normal programming resumes then it's fine.
Isn't it normal/healthy for weight to fluctuate by +/- 7lbs anyway? Or so my GP says.