(HealthDay News) -- Seasonal affective disorder (SAD) refers to bouts of depression that usually occur during the fall and winter, and tend to improve in summer and spring.

The U.S. National Library of Medicine says warning signs of seasonal affective disorder may include:

  • Feeling tired and having difficulty concentrating in the afternoon.
  • Feeling hungrier than usual, and gaining weight.
  • Sleeping more than usual, and feeling sleepy during the day.
  • Losing interest in work and hobbies, and generally lacking energy.
  • Withdrawing socially.
  • Feeling unhappy and irritable.