Not that you care, but I have clinical depression. I mention that you don't care not to guilt-trip or ask for pity, but because it's true - you have a lot on your plate too, and it probably angers you that I bring up depression as a justification for letting things bring me down.
One of the toughest parts of dealing with clinical depression is that friends and family often don't understand it, and actually think less of a person for it. Like one is using it as an excuse to not buck up and pull yourself out of a rut. Unfortunately, it is misunderstood. When stressors occur, the brain can start to get depressed (not sure what happens chemically here). To balance this effect, the body releases chemicals into the blood (I know of two, epinephrine and serotonin) as "mood lighteners." However, for whatever reason, sometimes the body doesn't produce enough, or maybe cells re-upload (remove from the bloodstream) the chemicals too quickly, and one moves from "normal" depression (i.e., something bad that has happened in your life) to a prolonged depression that can bring one down, even when things aren't going too badly. Basically, your mood can't be "lightened," so it's perpetually "dark."
Luckily, when diagnosed, one can take anti-depressants. I don't know how all of them work, but the ones I've taken, including Cymbalta, which I am currently on, operate as re-upload inhibitors; they prevent the cells from re-absorbing the mood lifters from the blood as quickly, attempting to balance the affects of depression using the body's natural solution. Here, dosage can be tricky. If the anti-depressant dosage is too small, the effects of the drug will wear off too quickly in comparison to the imbalanced system, and when it wears off, the depression comes back in full force. If the dosage is too great, the patient's mood will be over-mellowed - almost emotionless - which can add its own problems to the situation (low reaction times, feelings of lifelessness, etc.).
All I can assume is that people just don't understand the lack of control I have over it. It is assumed that I should be able to flip depression off like a switch; folks get tired of me having this problem, so they get mad at me for it. Particularly when most of the time, because of medicine, I am fine.
So I'm just venting it here, in the middle of the Internet.