I've known I have Seasonal Affective Disorder for a couple of years now. When autumn kicks in, I get depressed, apathetic and so, so sleepy. It's like an urge to hibernate. It doesn't help that I also suffer from Delayed Sleep Phase Syndrome (a.k.a. permanent jetlag), a circadian rhythm pattern screwup that, for reasons of my fucked-up body chemistry, is only controlled through strong sunlight. When the sunlight levels drop, the two disorders couple together to make me very broken for a couple of weeks, until I adjust.
So for the past week, I've been waking up at 12pm when my lightbox alarm clock sounds, then I've been lying in bed for a further 2-3 hours with the strong light streaming into my face and the clock sounding every so often. My body feels leaden - so heavy that I can't make myself move easily. Eventually, I get to the stage where I've had enough light on my skin that I feel agitated, which kickstarts my pulse rate to the point that I can get up. This is entirely normal for me at this time of year, and yes - the best that modern medicine can do for me. If I didn't have the lightbox & multivitamins & antidepressants, I probably wouldn't be able to get out of bed at all.
I will be more functional in a few weeks. In the meantime, I have to remember that the depression I'm feeling is more of a physical health/adjustment thing rather than a sign that something is terribly wrong. According to the various mental health indicators, I'm not actually suffering from major depressive disorder anymore. But I still have dysthymia and SAD and premenstrual dysphoric disorder (PMDD) giving me hell, plus the chronic anxiety I can't shake off. That doesn't make me mentally healthy, it just gives a timeframe for the depression.