There is a tendency to use the word depression to describe periods or episodes of sadness that each of us experience from time to time. And for many of us, during these periods it is not always easy to discern where normal sorrow ends and clinical depression begins. Yet, anyone who has ever experienced an episode of major depression knows-at least after the depression has lifted-that what they feel is more than just ongoing or persistent sadness. According to doctors, clinical depression is an illness characterized by a cluster of feelings, thoughts and behaviors that are remarkably distinct from a person's normal range of feelings and functioning. Caused by a complex interaction of biologic, psychological and social factors, a major depressive disorder can make a person extremely sensitive to life circumstances, the least of which can throw him/her into total loss of hope. During a major depression, someone can become surrounded by feelings of sadness, hopelessness, helplessness, and emptiness, and these feelings can distort every thought and experience, making life seem hopeless and unworthy. Feelings of being deeply and continually deprived, unworthy, insignificant, and guilt-ridden build on feelings of sadness. At the same time, a person may feel chronically irritable, often exploding into anger and frustration. While a major depression may be triggered by some life event or circumstance, a person's mood reaction may seem greatly exaggerated. However, depression has less to do with life's events than with an individual's existing vulnerability to the condition. In some cases, someone may experience a major depression as a single episode, but in most cases, clinical depression tends to recur periodically, reactively or cyclically. A major depressive episode could possibly last up to 2 or more years. When someone experiences milder depressive episodes, this is called dysthymia. For someone suffering from dysthymia, certain life circumstances, such as loss of a job, divorce, or relocating to a new environment, may provoke a much deeper depression. For some individuals, there is a seasonal component to their depression called Seasonal Affective Disorder (SAD). This is a form of reactive depression that is more prevalent in northern parts of the country where climatic extreme changes are greater. SAD usually affects people in the fall or winter and is characterized by fatigue, carbohydrate cravings, overeating, lack of energy or motivation to do activities normally enjoyed, and over sleeping. While the exact cause of SAD is not certain, it is possible that it may be related to the way in which the light responsive pineal gland in the brain functions.