My biggest triggers during the holiday season are the social aspect of holidays, and the pressure (whether self-imposed or otherwise) to Enjoy Everything Before It's Too Late.
My husband and I have over the years pared things down to a managable level. We have two small kids, so by default, Christmas is all about THEM now. We don't go to any parties, we don't exchange gifts with everyone and their brother, and the shopping is FUN as long as we start early and make lists. It's so much more enjoyable for me now that I know how to be organized about it, and now that I know how to focus on the little things that make the season special for my kids. For example, they love Christmas music. So, instead of getting all stressed out that the radio stations play 24/7 Christmas music starting in early November, I actually embrace it and let my kids get their fill.
I also build up the excitement of little treats (which under some circumstances is probably not healthy, but if you saw my son's pure joy at getting to eat a small crunch Santa, you'd understand!). I love little treats, too, so I set small goals and reward myself accordingly.
For gift-giving, I used to put a lot of pressure on myself to be the cool aunt who gives good presents. That's just too hard for me to deal with, so I've decided to become the cool aunt who gives cash. I've let go of the fear that it seems lazy - the "cool, thanks" mutterings of teenage boys is far more satisfying to me than an "oh." (My nephews are good kids, they're just typical teenagers!)
Finally, we do host my husband's side of the family here, but we set the bar very, very low. I hate hosting as a general rule, but for christmas we just do bagels and coffee, and the family knows not to expect anything more involved. I've found that managing expectations plays a huge role in my ability to cope and enjoy the holidays.