What Is Depression?
While everyone feels sad from time to time, if that occurs most days for more than two weeks, it could mean that clinical depression is occurring. Major depression is a period of sadness, irritability, or low motivation that occurs with other symptoms, lasts at least two weeks in a row, and is severe enough to negatively affect one's life. Depression is not a sign of weakness or a character flaw. It is a real and treatable medical illness.
These PET scans of the brain indicate low activity in a person suffering from depression compared to someone who is not depressed.