SAD stands for Seasonal Affective Disorder. It affects approximately 10% of the population and more commonly women.
Symptoms generally become apparent as the seasons change from Summer to Autumn when daylight decreases and our serotonin levels also decline.
Serotonin is a brain chemical produced on waking which keeps us alert, focused and our mood uplifted.
In SAD sufferers, the reduced daylight may cause symptoms similar to depression.