The holiday time with all of the lights, the general excitement, does penetrate their consciousness and I am wondering if that is part of your child’s dysregulation this month. To keep things moving forward you might want to consider keeping it low key, regular bedtimes, no change in diet (i.e. keep the treats low), etc.
One family whose child could not stand the excitement, showed the child her gifts when they bought them, then wrapped them and told her what was in the packages. They opened one a day and talked about what was in the other packages throughout the Christmas week. The element of surprise is sometimes just unbearable. So is the frantic unwrapping of gifts. All of those things that we feel make the season just lovely and magical can throw sensitive kids into a very bad place.