Depression is characterized by sadness, loss of interest in things once enjoyed, low self-esteem, suicidal thoughts, hopelessness, feelings of guilt, fatigue, difficulty concentrating, anger/irritability, physical complaints (ie: stomachache, headache), changes in sleeping and/or eating patterns. There are several theories on what causes depression and therefore treatment is varied as well. Therapy may include addressing unhelpful thoughts, creating a daily schedule, or addressing the specific situation that lead to the depression.