LOL, you didn't like the thoughts I gave about depression. Well, I don't have personal experience with depression; but I have studied (not to degree level) about neurotranmission and some of the various DSM disorders (Major Depression, Cyclothymic Disorder, etc.) The bottom line is that in some people, serotonin, norepineprine, or acetylcholine can be out of balance because of bad diet, disease, or drug/alcohol abuse which damages neuronal membranes and thus, neurotransmission. In other people, they may have learned bad habits or ineffective coping skills which facilitate some negative thought patterns.
But, in almost every case, there is a basic loss of equilibrium, hope and focus. Completely deflated or frozen by anxiety. No goal-setting. No focus on activity outside of oneself. I've seen this in some family members. The focus on self is a huge part of the problem with depressives.
Regeneration is, by far, the best answer to that, and I've seen people get better because their prayer life improved and they got busy, working around other active, healthy people. Activity (including strenuous exercise) does a lot to increase neurotransmission, and working hard toward goals slowly repairs the neural pathways in the brain, as well. Staying off excessive booze and hard drugs is crucial, too. Fellowship, prayer, and service can take one a long way toward keeping up the activity level all week, and I've seen those things help depressed people tremendously.
Let's face it: Psychology and Psychiatry over the last 100 years has been a failure. They are a total bust. Few would argue that people, in general, are healthier or more mentally stable now than even a few decades ago. There used to be a time when you gave someone a pep-talk and a kick in the pants, and that's all it was expected to take to get them moving. Now, we have more labels for all the disorders, and more ways to "treat" them, but with abysmal results. Too many people have become comfortable carrying a label for life, instead of looking forward to the day when they are fully recovered. Christians need to do better than that.