Is your depression seasonal by any chance? Mine always goes downhill when the days start to shorten and the light levels drop.
It is connected to the seasons, but not in the usual manner. Living in Sweden, the days have been significantly shorter for some time already (after a near-nightless summer), though there is still plenty to go. If it is related to the light level, then either the threshold before something happens lies quite low, or the reaction is delayed. The strange thing is that I never consciously mind the darkness, and in fact find it somewhat comforting.
The depression goes in intense periods lasting a few hours to a day, of which I am about to have gone through the most intense so far this season, between which I largely feel fine. Those periods grow in intensity and frequency until a gradual decline eventually occurs.
There are two periods of such periods; mid-autumn to mid-winter and mid-spring to early summer. The current one is the milder one, during which I become most emotionally unstable. The other one is the most severe, during which I last year became completely emotionally numb.
