Major depression has a number of defining factors—mostly having to do with withdrawal, though agitated or atypical depression may have an intense negativity rather than a flattened passivity—and is usually fairly easy to recognize; it deranges sleep, appetites, and energy. It tends to increase sensitivity to rejection, and it may be accompanied by a loss of self-confidence and self-regard. It seems to depend on both hypothalamic functions (which regulate sleep, appetites, and energy)
