You probably know the feeling. Mornings get darker, the alarm feels heavier, and by late afternoon you just want to crawl back under a blanket.
For most people the slump lifts once the days stretch out again.
For about 5 percent of American adults, that drift is not just the winter blues.
According to Cleveland Clinic, it meets the clinical bar for seasonal affective disorder, a form of depression tied to the shorter days.
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A further 10 to 20 percent get a milder version. The condition typically runs four to five months, beginning in late fall and lifting in spring.
The shorter day hits the brain
The National Institute of Mental Health says people with winter-pattern SAD have reduced serotonin, the brain chemical that steadies mood.
They also produce too much melatonin, the hormone that tells the body to sleep. The two shifts drag energy down and make mornings heavier than they should feel.
Common signs are oversleeping, carbohydrate cravings, weight gain and a loss of interest in things that usually feel good.
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Welltica has walked through the eight warning signs most people brush off as winter blues.
The light therapy
The first-line treatment is light therapy. The NIMH describes a 10,000-lux light box used first thing in the morning. A session runs 30 to 45 minutes and is kept up from fall through spring.
A 2026 systematic review in the Journal of Affective Disorders Reports pooled randomized and crossover trials of light therapy for seasonal depression.
The authors recommend at least two weeks of daily sessions before judging whether it is working.
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Vitamin D and exercise
Other winter remedies hold up less well. The National Center for Complementary and Integrative Health has reviewed the trials.
It reports that vitamin D supplements are not considered an effective SAD treatment on their own, with mixed results across studies.
Exercise fares better. One trial the center cites found that light therapy and physical exercise, alone or together, were well tolerated and both eased symptoms.
Cognitive behavioral therapy adapted for SAD may hold on longer. A head-to-head trial the center summarizes found CBT-SAD outperformed light therapy two winters after acute treatment.
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The mood dip is worth a doctor's visit
If low mood, oversleeping and loss of interest come back every fall and interfere with work or daily life, raise it with your doctor. Antidepressants are an option alongside light therapy, and ruling out other causes of fatigue matters.
Light boxes labeled 10,000 lux and marketed for SAD are available over the counter in most US pharmacies and online retailers, often with timers that match the recommended morning window.
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This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.