Having grown up in an areligious, non-Christian yet Christmas-celebrating family, I don't have much problem with that particular conflict. To me, Christmas works perfectly well as a secular holiday, a great time to see friends and exchange tokens of affection and attend parties and eat delightful foods and decorate the house and put up a tree and lights lots of candles and wear festive clothes ... all activities done purely for their own sake, because they're fun and pretty and heartwarming.
My own Christmas problem is my sons. Their tastes are narrow and their expectations are high -- they've never played much with toys, even when young, so it's always been a little tricky to find things they like. But now, at 11 and 13, they are mainly interested in electronics and sporting equipment, stuff that's way out of my budget. Add to that the fact that I'm the one doing the shopping and I'm not the best judge of young boys' tastes. Yet they really want to be surprised and excited on Christmas. A couple of years ago, the last year we sort of kept up the pretense of Santa's existence, they hated almost everything I got them. They tried to be polite, but their disappointment was obvious. Christmas was genuinely ruined for me.
BTW, I get Seasonal Affective Disorder, too. Mine doesn't really kick in until after the holidays, but it lasts until mid-March. The most effective treatment I've found for it is to get outside every day, especially if it's sunny. Often, you can feel your mood lift as quickly as if you'd taken a pill. If it's too cold to take a walk or go skiing or skating or whatever, drive a car with a sunroof.