I have been struggling the last few days with feeling sad. This isn't new: I have experienced recurrent bouts of depression since I hit puberty. As I've gotten older, they have diminished markedly in both length and intensity, but it is still something I occasionally suffer through.
Depression is not something that makes rational sense. While usually there is some sort of trigger for a mini-depressive bout (a marital fight, bad news, sickness, a life disappointment, stress), often triggers will happen and I won't get depressed. And the severity of the trigger isn't really correlated to the severity of the depressive episode. It's more like catching a cold: sometimes you know how you got it, but usually it's just random.
Once you have become depressed, rationality has definitely left the building. Everything is now filtered through the greyish haze and lack of all energy, hope or initiative which characterizes this mental state. It also tends to be self-perpetuating: often I actively seek to prolong my stay in depression's netherworld, by refusing to do things which might improve my mood (like exercise, or seeing people), and attempting to put a negative spin on anything positive that might occur (like saying "People are only nice to me because they feel sorry for me. I must be such a loser."). The only properly functioning section of my brain is the one which perceives potential problems or downsides: every little bad possibility appears in my brain with great clarity and insight.
Because depression isn't rational, using logic to fight it doesn't work. Instead, I find the only solutions are 1) distraction (because my brain can't dwell on everything bad if it is busy with some other task); 2) proper self-care (getting enough exercise, sleep, healthy food and positive social interaction); and 3) constant self reminders that being depressed is just an emotion, and like all emotions, will change soon (since one of the worst things about being depressed is that you feel it has always been, and will always be, this way).
Luckily (?), I am fairly moody, so while my emotions can be very intense, leaving me in tears curled up in bed telling B I wish I was dead, in a few hours or days, I feel completely differently, and am again ready to face the world with courage and optimism.
I like remembering this song at times like this.