Depression is actually a symptom and there are various causes for this. Just like a fever is brought on because of an infection in the body or heart trouble is because of the malfunction of your circulatory system, depression is a feeling of utter dejection because your body cannot cope with some kind of stress which it is going through. This could be either mental or physical. The depression could be caused by one of several disorders or by more than one. There are anxiety disorders, eating disorders; substance abuse brings on disorders like depression and other more severe causes.
Signs of depression could start with some event which is disturbing or sometimes with no apparent reason or cause. The former is easily treated as the cause is known but the latter has to be diagnosed more carefully. A person may find himself depressed for no reason at all and will have to cope with it until others realize that he or she needs help. Most people are not sympathetic to such sufferers and it is only when the symptoms become very acute that they realize that the person needs help.
Diagnosing the type of the depression which the person is suffering from is half the battle won. The person may have a major depression problem, or a dysthymic disorder, a cyclothymic disorder, a bipolar disorder which is a manic depression, a unipolar depression and a psychotic depression. Each of these depressions in turn could be severe, moderate or mild and the treatment would depend on this degree of severity and other signs of depression.