There are "dark times" from my adult life that I wouldn't post online for a number a very varied reasons. One that stands out (and that I WILL) put online is being separated from my mother when I was in first grade and she was hospitalized for a lung infection for about eight months. My father and aunt were great and did their best to care for, and keep "happy enough", three young kids - including a toddler); but for children to be away from their mother for eight months out of a "childhood year" is a long stretch of "dark".
We could talk to her on the phone (obviously, no cell phones or Skype in the late 50's) and see her on Sunday afternoons (when the weather was good enough for us to stand outside her window and talk to her from there). Needless to say, that wasn't a whole lot of help with "the dark thing".
Since mothers' biggest concerns are always (at least in the case of mothers who are good mothers and close to their children) ones to put what their children are dealing with, and whether they're OK and safe and healthy, I know that, combined with her own health worries, and worries about "leaving behind" three young kids, made that a horrible time for my mother. She once said it helped her to know that my father was as close to us, and as good with cooking/cleaning as she was, and she'd joke that he "was worse than" she was as far as not taking foolish chances with kids' safety went.
Something else that probably helped her deal with the situation from her own end of things (as opposed to ours) was knowing that there was a set way for handling that particular infection (hospitalization). In other words, there was a solid reason for the situation, and she (or we) couldn't/shouldn't blame anyone for it.
Fortunately, she returned home and live until I was past forty. With Mother's Day being tomorrow, when I think of my mother it certainly is not, at this point, anything related to that eight months I spent without being with her (of course, eight months from an adult's set of eyes doesn't seem as long as it does to a two-, six-, seven-, or eleven-year old). It's instead about all the rest of the time that I was growing up.
Maybe I chose this as my "darkest thing" because I know that so many things seem so much darker to children than to adults. When you're an adult you can pretty much deal with most things as far as your own "darkness" goes. It's a lot bigger when you're a kid (or maybe at least until you have your own children).