Depression

Depression, especially chronic depression, seems to be something that either you understand because you have experienced it, or you cannot understand because your "blue funks" have never lasted more than a day or so.
I am in the first category, and I envy those in the second.
Trying to describe it is mostly an exercise in futility, but here's my latest attempt.
Find a gym with a special kind of track. It's kind of like a fifteen-foot-wide wooden bowl, and the idea is for you to run in circles around it. It's based on the same tricks of physics that let motorcycles ride upside down on the inside of large steel cages, though I've never heard of any human with the leg-strength or stamina to let them pull that off. Anyway, the workout this track provides gets progressively worse the faster you run. As you accelerate, you can run higher up the side of the bowl, but your own inertia pushes you harder against the track. Most models have lines on the sides to tell you how much 'gravity' you're inflicting on yourself, based on how high up the side you are.
Run a few laps, see if you can get up to 2.5 gees, and pay attention to how it feels.
Now stop, stand in the middle of the track, and imagine that you're still feeling that 2.5 gees pulling you down.
Go ahead and fight it. Remember what it felt like to move from 1 gee to 1.5, then to 2, then to 2.5. Try to imagine what it would be like to go faster, to feel even more gravity pulling down on every part of you.
For you fitness buffs, who take that sort of thing as a challenge, you're missing the point. Try imagining those gee-forces pulling on you every waking moment. It's worse than "The Wall" experienced by long-distance runners; that's just your body telling you that it's run out of freely-accessible carbohydrates to burn for fuel, and now it's started to burn through your reserves of stored fat. As I understand the phenomenon, it's possible for runners to train themselves not to react emotionally to it, but there's no way to avoid the discomfort.
Depression is like gee-forces that never give up; your muscles never strengthen enough to stand up to them because they never get the rest they need to repair the damage.
Depression is like the Wall that you cannot burn through, no matter how hard you push.
Depression is a collection of different things that science is only now beginning to understand, and I pray to whatever gods there may be that I live long enough to avail myself of the new treatments just being popularized.
But depression is as patient as the oblivion whose clothing it has borrowed, and as merciless as gravity.
Those of you who have never felt it, count your blessings.
Those of you, my brothers and sisters in suffering, who understand... I pray that you continue to find the drips and crumbs of hope you need each day.