The darkest hour for an individual, I believe, comes when you recognize/admit/accept that we aren't who we portray we are.
It often comes at a time when people close to us make the connection... see our actions, hear our thoughts, and realize we aren't who they thought we were. Turning their world around.
Its when we know we have been seen. We can hide our faults from ourselves, we can even deny we have any at all. We can find other things (religion,drugs,alcohol,sex,sports,gambling) to hide behind. People can even know us as an addict, but, not know why. It is the shame and guilt that pushes us to portray ourselves in a light we think is more like-able to others.
But the moment we concede, the moment we have no choice but to admit who we are, to accept we have been fraudulent all this time, to give in and let it be known... for many this is the darkest hour.
It is also, ironically, the brightest hour of our lives. To be free of all the lies, disgust, anger, shame, and to grab on to the real us. Freedom... finally.