Depression is a serious mental and emotional illness that affects 5-8% of the population. Major depression is persistent and can significantly interfere with an individual's thoughts, behavior, moods, activity and physical health. 

Other depressive disorders include: dysthymia, which is a less severe but chronic depression; bipolar depression, which is the depressed phase of bipolar disorder; and seasonal affective disorder which affects people who live in geographic areas where there is little sun.

Symptoms of depression include: a persistent sad or irritable mood; pronounced changes in sleep patterns; changes in appetite and energy; difficulty thinking, concentrating and remembering; physical slowness or agitation; lack of interest or pleasure from activities that were once enjoyed; feelings of guilt, worthlessness, hopelessness and emptiness; recurrent thoughts of death or suicide; and persistent physical symptoms that do not respond to treatment such as headaches, digestive disorders and chronic pain.

Depression can be effectively treated with medication, psychotherapy and in severe cases, ECT (Electro Convulsive Therapy). For seasonal depression, light therapy can be helpful. Psychodynamic psychotherapy  CBT, and EMDR have been shown to be effective for treating depression. EMDR  can be used to enhance a person's self esteem. Usually a combination of psychotherapy and medication produces the best results; and the effects of psychotherapy last longer than medications; as depression tends to reoccur once medication is stopped.