A depressive disorder is not a passing blue mood. It is not a sign of personal weakness or a condition that can be willed or wished away. Without treatment, symptoms can last for weeks, months, or years. Bipolar depression includes periods of high or mania. Not everyone who is depressed or manic experiences every symptom.
Some people experience a few symptoms, some many.
Also, severity of symptoms varies with individuals. This is a most serious type of depression. Many people with a major depression can not continue to function normally. This is a mild, chronic depression which lasts for two years or longer. The person may not realize that they are depressed.