Depression usually develops over a period of weeks or months.
The person may not even realize that he or she has become depressed. Depression, a health problem, is different than grief. Grief is the normal response to loss and involves changes in mood, activity and bodily processes but is not as extensive as depression. Depression affects the person's health, interpersonal relations, work, and ability to enjoy life. They may appear moody or irritable to others, not go out with friends, and lose interest in romance.