How does depression vary?

Here you can see clearly how depression can vary:

• You may have depression just once in your life.
• You may suffer from depression several times in your life.
• You may suffer from bipolar disorder (also called manic depressive disorder) and suffer both bouts of depression and mania. 
• Your depression may manifest itself as a relatively minor episode, where your spirits are lower than normal for a while. You find it hard to sleep and you lack energy, but otherwise cope at work and with other responsibilities.
• You may suffer from moderate depression - you are constantly sad, lack energy and lose interest in what's going on around you.
• You may suffer from severe depression, which has brought your life to a halt. You can't and don't want to do anything or be with others. You may even become psychotic, be out of touch with reality and suffer from unrealistic feelings of guilt.

Each diagnosis has a number of characteristic symptoms, which are known as "diagnostic criteria".

If you have a certain number of these characteristic symptoms, you are diagnosed as suffering from a specific affective disorder. The most common mood disorder is depression and is termed a "depressive episode" as defined in the Diagnostic and Statistical Manual for Mental Disorders, the fourth edition (DSM IV). Read more.