Seasonal Affective Disorder
Diagnosis

Seasonal affective disorder (SAD) can be difficult to diagnose because it's hard to differentiate from other forms of depression. Your doctor will ask about your symptoms and how long you have been experiencing them — in particular, whether you've experienced symptoms of SAD for at least two consecutive years and whether it was during the same season each year.

In addition, your doctor will want to know if the periods of depression were followed by seasons when you did not feel depressed. Lastly, your doctor will want to make sure that there are not other explanations for the changes in your mood or behavior.