There are four main types of depression. Major depression is characterized by severe symptoms that don't go away. Without treatment, episodes can last as long as 18 months. People who have this once often have another four to six episodes in their lifetime. Dysthymia is a milder but longer-lasting type.
Episodes often last more than five years.
It's not totally disabling, but it robs people of their ability to function well and enjoy life. During manic phases, the victim's judgment suffers at the same time their self-confidence shoots to unnatural heights, resulting in reckless behavior like spending sprees or risky sexual encounters. Seasonal affective disorder typically occurs during winter. Scientists don't know the cause, but think it triggers depression because the brain produces more of a mood-controlling hormone called melatonin when sunlight levels are low. Sometimes depression occurs in episodes, with long periods of normal functioning in between.