Major Depression is a mood disorder characterized by persistent feelings of sadness, apathy, hopelessness, and fatigue. People of all ages can have it and its onset may occur without a trigger. Early life experiences may be a contributing factor, which is a topic that psychologists often explore.
Depression is a complex set of symptoms all of which are believed to arise as a result of environmental factors (e.g. loss of a loved one) and genetic factors (e.g. serotonin unbalance).
The standard treatment for depression symptoms is Cognitive Behavioral Therapy (CBT) and it can be provided by psychotherapists and psychologists. Psychologists are also equipped with the ability to diagnose depression.