Seasonal affective disorder (SAD) is a form of depression that occurs in relation to the seasons, most commonly beginning in winter.

Seasonal affective disorder (SAD) is marked by symptoms of depression profound enough to seriously affect work and relationships. The disorder may have its onset in adolescence or early adulthood and, like other forms of depression, occurs more frequently in women than in men. Most people with the "winter blahs" or "cabin fever" do not have SAD.

The cause of SAD is not known, but is thought to be related to numerous factors including body temperature, hormone regulation, and ambient light. A rare form occurs in the summer.

• Depression with the onset of fall or winter
• Lack of energy
• Decreased interest in work or significant activities
• Increased appetite with weight gain
• Carbohydrate cravings
• Increased sleep and excessive daytime sleepiness
• Social withdrawal
• Afternoon slumps with decreased energy and concentration
• Slow, sluggish, lethargic movement

A psychological evaluation rules out other causes for the symptoms and confirms the diagnosis.