But chances are, there's a whole lot more to your SAD story. Before you flip on a light box, make sure these other seasonal mood-busters aren't dragging you down.
Cold temps make it all too easy to curl up on the couch and let your gym habit slide, but it's common knowledge that regular exercise holds the power to lift your spirits.
"Moving around is helpful to everyone's mood," says Harvard psychologist Dr. John Sharp, author of "The Emotional Calendar."
You don't even have to commit to a full-on routine. In a study published in Perception and Motor Skills, researchers found that even a single exercise session at any intensity can increase positive mood feelings and decrease the negative ones. If you live in a wintery clime, take advantage of the snowshoeing and ice skating to shake up your exercise routine.
You're worried about money
Holiday expenses take a bite out of your bank account, and fretting about credit card bills can rob anyone of good cheer.
Before you start racking up the bills, decide if expensive gifts are even necessary. A homemade present can mean much more than a pricey package.
"Don't be afraid of the B word: a budget," says Sharp. "It can be a big or a small number. Spread it around in a way that can make you happy, but don't put yourself in the hole."
You're overwhelmed with family obligations
'Tis the season for familial gatherings -- and all of the holiday stress and drama they can bring.
But guess what? It's entirely within your power to decline any stress-inducing invites. If you'd rather not trek to Aunt Linda's house three hours away for a holiday dinner, politely say no by saying you're eager to start making new holiday traditions at home. And if you just can't avoid sitting next to a relative that drives you crazy, take a deep breath before engaging in conversation with her: Research from Harvard Medical School shows it decreases tension and anxiety.
You're not eating right
Chowing down fattening holiday foods you don't normally eat and skipping your usual nutritious fare can leave with no energy, says Jane Ehrman, a behavioral health specialist at the Cleveland Clinic. Make this a rule: If you're hitting a party in the evening, eat only fruits, vegetables, and lean protein during the day. The antioxidants, fiber, and protein will fuel your body -- and help keep a well-balanced mind.
You feel left out
While some people are running ragged at the holidays -- dashing from recital to party to neighborhood caroling -- others have a lot of unwanted time on their hands, particularly those who don't live near extended family.
"Holidays are oftentimes easier for couples and families, and if you're by yourself, you may feel alienated this time of year," says Ehrman.
If you're feeling blue about sitting on the sidelines, make a difference by volunteering at a nursing home, homeless shelter, or hospital -- you'll be helping yourself as much as others.
You're drinking too much
If seasonal revelry has upped your alcohol consumption, then you may notice you're feeling draggier than usual when the alarm clock chimes in the morning.
It's not just about hangovers: a study published online in the journal Alcoholism: Clinical and Experimental Research found that although booze may help put you to sleep, it prevents you from getting high quality rest.
"If you go to a holiday party with wine being poured, it's hard to keep track of what you're drinking," says Sharp. Be clear with yourself: Nurse one glass of Pinot Noir as long as possible, then switch to water.
The holidays are a magical time for kids, but the adult realities of bills, shopping, wrapping presents, and meal prep don't instill the same sense of wonder.
"As a child, it's about the parties and cookies and presents," says Ehrman. "As the grownup, you're responsible for all the background mechanics a kid is never aware of."
If you feel the holidays have lost some of their spark, try to reconnect with your childhood memories. Chat with a sibling about shared experiences or pop in an old home movie to stir up happy memories.
People are usually pretty busy all year, but the end-of-year wrap-up can be particularly hectic, leaving you frazzled, stressed, or just plain worn out.
"People don't always realize the amount of stress they experience this time of year," says Ehrman.
Not sure if you've got too much on your plate? Here's a way to tell: "If you get excited when something gets canceled, you've got too much going on," says Ehrman. When your plate is too full, take something off.
You're turning into a hermit
Cold weather and treacherous roads provide the perfect excuse to cancel your evening plans and veg out in your jammies.
But if you're the type of person who thrives on social stimulation, being a homebody could be bumming you out. A study of more than 33,000 people published in the Journal of Clinical Psychiatry found that social isolation puts you at greater risk for mental health problems.
Resist the urge to bail on dinner with a friend or skip a favorite group exercise class. Pull on your snow boots and forge ahead with activities that put you in contact with other people.
Your expectations are unrealistic
"Happiness in life really is about expectation management," says Sharp. If you think every meal, present and decoration is going to be absolutely perfect, you will always be disappointed.
Figure out what works for you, and make the right adjustment. "You can't change the fact that you're going down a river, but you can paddle to the left or the right to avoid the big boulder," says Sharp. "That makes a world of difference."
This article originally appeared on Health.com.