Creativity is hard to categorise. However, it also isn't completely random. When I'm working on a project, I can get myself into "daydream" mode and gently steer my creativity to find answers to the question or problem at hand, so I would guess that even if it is random firing of neurons, it is random firing of the neurons active at that moment. This means that it certainly is NOT random, because you can choose what to think about, and hence, steer that random firing to get a result. Evolution likes that.
With e.g. schitzophrenia, I think that people who have a double copy of the gene and have a high(er) IQ are more likely to find a way around the problem and deal with it. I would guess I'm one of the lucky guys with a double expression of the gene, but also with a good IQ. A lot of what was said was very recogniseable - I've fought with depression, burnout and more, and also had an immense war between myself and my own mind, and have seriously questioned my sanity, before I finally learned to detach from my thoughts and emotions, and stand behind them as it were instead of being dragged along with them on a very rough rollercoaster ride. Meditation, sports, the forced responsibility of having to run my own company and lots of research saved my sanity. Now my creativity is a tool, a part of my mind which can be accessed at will instead of a scary the-voices-say-the-universe-hates-you personal enemy you can carry everywhere you go. I am the eye of the storm, as it were, and it is no longer easy to rip me loose - I would guess that only a long, sustained depression combined with stress over a period of years could do that (because it means that slowly but surely your belief in yourself and your self-imposed structure will be eroded by the negative emotional flood from the amygdala).
I think the problem is compounded once you get depressed. It seems to me that creativity is rampant throughout the brain. When I was depressed, it seemed that my "logical" brain was less active and my "emotional" brain ran the show - all my reactions were negative and emo. This might be because the amygdala seems to "shout louder" at certain times than others, or maybe the rest of the brain is more overwhelmed by its "voice" during depression because it is less active, I don't know. At any rate, it means you are completely at the mercy of emotional reasoning and the torrent of feelings because you don't have your "logical net" to tell you "nah, I'm dramatizing again" and you simply shrug them off as an itch.
At any rate, I know a few others like myself and their stories are similar: mental override, take control, avoid pitfalls of deep feelings (unless they're positive, and even then keep an eye on them), and view the world as a statistical game instead of a personal interaction. The latter is probably the most important, because once you start trying to ascribe a (negative) personal meaning to the events that influence you - for example: "God made me lose my job because I'm bad / worthless / whatever", then you open Pandora's Box on your own mind. That's also one of my warning signs that I may be stressed out or in a downward spiral, and that I need to take more breaks and relax more: if I find my mind trying to reason like that, I know I'm in the danger zone, so I adjust for it. Not doing so probably means you'll end up creating another religion based on frustrated depression.