No, we don't have to panic every time we find ourselves screaming at the drawer in the kitchen that constantly sticks or snapping at a friend on a bad day. Irritability comes up in the normal course of life.
But it turns out that having overt irritability and anger during a depressive episode is a significant indicator that a strong or persistent depression will occur [source: Judd et al.]. One 31-year-long study led by University of California San Diego scientists indicated that people -- even those who didn't have more episodes of major depression before the study -- who had displays of irritability and anger were more likely to later have chronic, severe depressive episodes as time went on [source: Brooks]. Now note that it wasn't just an occasional crabby day that put a person in this group. Subjects had to acknowledge that they were "somewhat argumentative," "quick to express annoyance," would often lose their temper or shout, or were even "repeatedly violent" [source: Healy].
Even more interesting, those with irritability and anger also had a higher rate of anxiety disorders and substance abuse. The study's authors even suggested that depression that featured irritability and anger might be diagnosed and treated differently than your run-of-the-mill major depressive disorder [source: Healy]. If you do find yourself far more prone to irritable or even hostile behavior, there's a chance you're not just unhappy -- you're depressed.