I've been depressed recently -- maybe not suicidally depressed, but depressed enough to think about it a lot* -- and for me it's absolutely a balance of fears. The weights of past regrets and past failures, the fear of facing them, the fear of future failure (I'm co-founding a slowly failing startup now), the fear of disappointing or alienating loved ones -- they all gang up and become completely overwhelming. The passage above captures it pretty well, though I haven't ever gotten to the extreme it's describing.
Exercise and sleep help.
*I have enough people who love me and depend on me that I know I'll never act on it, but it has become something I fantasize about probably a couple times a day, and many times more on bad days.
I don't have a solution, just an observation. I think your mention of the word "overwhelming" is very important. If there is a solution, I think it will be found in non-destructive (not drugs, not sleeping all day, etc.) changes in lifestyle, values, and focus--things that vary a lot from person to person and probably require experimentation--that prove effective at reducing the emotional feeling of being overwhelmed.
Also, it seems that "overwhelm" is what happens when we combine several bad things that don't have to be combined (various fears, various regrets, disappointments, etc.) into a single, nasty package viewed all at once. Finding a way to focus on them separately really reduces the magnitude of the overwhelm.
I should've pointed out that the experience of depression varies from person to person, there's a set of symptoms of which only a subset might be experienced.
For most people depression is treatable and manageable. Make time to see a doctor. Simply not having to keep yourself afloat in tar is worth it.
Exercise and sleep help.
*I have enough people who love me and depend on me that I know I'll never act on it, but it has become something I fantasize about probably a couple times a day, and many times more on bad days.