Whether for reasons of hormones, body chemistry, silly thoughts, or a reaction to reality, some days you're down, plain and simple. I find those days challenging to climb out of, not the least because there's the conflicting voices in my head.
One voice is telling me almost without words how colorless the world is, how tedious my moments on it, how I will never change to be like "the rest" of the world that accepts its fate and makes the very best of it, how I have "no right" to be sad when there are so many people far more worse off than me (a variation of the "clean your plate, there are starving people in China" saying).

The other voice, just as sneaky but more articulate, says "things will change, life is never the same from moment to moment," and "remember, these are just thoughts, they don't define you," and "count your blessings," and "walk your talk," and "get moving, your mood will change when you do," and "just try to keep the corners of your mouth up for a little while."
I can't complain to anyone about these voices, because that would be silly, they are in ME, not somewhere else. And I can't complain to anyone about the sadness and hopelessness that sometimes rushes over me, because I don't want to burden others who are just trying their best to get through these hard times and because what can they do about my problem anyway? Nothing. (Except a therapist, who could give me tips I intellectually know already from having read hundreds of self-help books since the age of 14.)
Now I understand the little outbursts I see on Facebook now and then. When I was in a better

mood, I merely thought "stop complaining, see the positive and you'll attract it to you." In a down mood I think, yeah, but for not being able to properly phrase my feelings in a Facebook blurb, I'd be there too.
I wish when I'm in my more in-sync, positive, I-love-the-world-in-spite-of-sadness-and-pain mood, I could be more compassionate toward others who are in the mood I'm in right now. At the least to acknowledge that yes, they are right, their lives are not unfolding as they thought they would and that times are hard, but to hang on, don't give up, plow onward, we love you.