Why does my dog get aggressive at night?

This excerpt may help: " Dogs who display owner-directed aggression most often behave aggressively in the evening hours. They are better tempered, less likely to be aggressive, in the morning. This may be because brain serotonin is highest in the morning and falls over the course of the day, reaching low levels in the evening as serotonin has metabolized to melatonin. So the supposedly dominant or conflicted dog is much less dominant or conflicted when he first wakes up and much more irritable or less sure of himself as dinner time approaches. This roller-coaster ride can be evened out by increased exercise, diet changes and various pharmacological strategies such as the use of serotonin-enhancing drugs..." http://www.veterinarypracticenews.com...