If I cant identify the usual triggers like not eating, sleeping missing meds or stress and I still feel depressed I try to break down time into shorter bits, like just deal with the rest of today-dont predict something about tomorrow or the rest of the week because it will probably be a negative prediction when Im feeling down and since no one can predict tomorrow anyway why get upset about it--its not possible to predict " a waterfall", its the sneakiness of depression-it gets a grip on us and we go in circles keeping it going, negative thoughts, little activity.  etc

 If I cant get out of it or Im eating sleeping etc, I have to do something that will change my thoughts and if possible occupy me and my head so I cant go over and over how bad I feel or why I feel bad, or what to do ,so on and so on and so on. It may be some physical activity outside if I can, anything, clean the garage, go wash my car, go to a bookstore/library and read something new--my thoughts have to get off the depression broken record- then I usually notice feeling better, not great just not as bad, painful feelings--its individual for everyone so try a few things and see what can work for you, i find the quicker i tackle feeling bad the better since it builds and builds on itself the longer it goes on as i'm sure you know--hope this is something to think about--i've found depression to be one of the sneakiest, slippery things i've ever dealt with- suddenly unexpectedly you start feeling down for no apparent reason- i try to jump on it-the best i can, post how you are doing and pass along any ideas, i always learn new things here  thanks  bc