Those are just the extremes. The holidays bring out all kinds of distress, dysfunctionality, and acting-out. Few are immune-- the hope of all the promised seasonal joy exacerbates life's unexamined unhealed disappointments and they come right to the surface-- "But you were SUPPOSED to..... [insert stored disappointment of one's choice).
Ask anyone in any of the helping professions who has to deal with people-- it's not just the busy-ness of the holiday season that tries one's patience and strains one's good will. It's the old baggage being flung about, sometimes with tremendous force.
Add to that the onset of SAD.... money worries.... seeing a year come to an end... the opening of tax season.... and it's like a colossal full moon.