Depression is a big step on the way to complete satanic control of a person. In it there is a broken spirit, one that is pressed down and crushed.
Being depressed for a long period of time is of the devil and not normal life. Depression is not of God and makes a person sick. The devil will take advantage of the person's mind moving in with conflict and confusion to destroy.
We must be like David of old and encourage ourselves in the Lord....Psalm 42:5 and Psalm 103:1 for example. By doing so the devil has to flee and we keep our mind stayed on the Lord.