Some people experience a serious mood change during the winter months, when there is less natural sunlight. This condition is called Seasonal Affective Disorder or SAD. SAD is a type of depression. Here are the symptoms of SAD: Sad, anxious or empty feelings. Feelings of hopelessness or pessimism. Irritability or restlessness. Loss of interest or pleasure in activities you would normally enjoy. Fatigue and decreased energy. Difficulty concentrating, remembering, or making decisions. Difficulty sleeping. Changes in weight. Thoughts of death or suicide. SAD is a serious condition – a subtype of major depressive disorder in which life can be severely compromised. Far more of us experience similar but less intense.