Holidays can be dark times for people, for a variety of reasons. Sometimes one simply feels put upon to feel happy or have fun just because the calendar says so. (This happens to me pretty much every New Year's Eve. I get quite grouchy about it.) Sometimes one is grieving a loss. Sometimes one is down in the mouth about a job, or a family situation, or an illness or other personal issue. Sometimes one is exhausted (perhaps about the job or issue or family).
In the last few years, some churches have been putting on "Blue Christmas" services some time during Advent, including on the winter solstice (these are called "The Longest Night"). At first the Blue Christmas services seemed geared toward those who are grieving a loved one (and so, for instance, the prayers specifically address that loss and grief) but apparently some liturgies are more generalized and speak to not only grief, but other pain, unhappiness, and depression. I have not attended a Blue Christmas liturgy but I would like to, both to see how it is done and to have a go at addressing my own feelings about being in a dark place during the holidays.
I think it is true to say that many people feel exhausted and anxious this year. It's important to own those feelings and also to try to make choices that will address (if not alleviate) them: eat healthily, get enough sleep, cut back on anything not necessary and/or life-giving, get some exercise, enjoy time with friends, hang out with the pets. It's just so easy around the holidays to get burned out even in the best of times, and this year with so many suffering from unemployment or underemployment, reduced income, getting the bills paid - the worry that those kinds of issues generate added to the already hectic and overscheduled full-of-probably-unrealistic-expectations holiday season can send one right down into the depths.
But know, too, that one is not obligated to be cheerful just because it's a holiday season. And doing "all the right things" doesn't necessarily get one out of that dark place. It just may make it all a little more bearable or manageable. Find a friend or confidante with whom to let it all out - you're not alone. Many people are sad during the holidays. You'd probably be surprised just how many are.