The ‘dark night of the soul’ is a term that goes back a long time. Yes, I have also experienced it. It is a term used to describe what one could call a collapse of a perceived meaning in life… an eruption into your life of a deep sense of meaninglessness. The inner state in some cases is very close to what is conventionally called depression.
Nothing makes sense anymore, there’s no purpose to anything. Sometimes it’s triggered by some external event—some disaster perhaps. The death of someone close to you could trigger it, especially premature death—for example, if your child dies. Or the meaning that you had given your life, your activities, your achievements, where you are going, what is considered important, and the meaning that you had given your life for some reason collapses.
It can happen if something happens that you can’t explain away anymore, some disaster, which seems to invalidate the meaning that your life had before. Really what has collapsed is the whole conceptual framework for your life. That results in a dark place.
Full article by Eckhart Tolle : https://www.eckharttolle.com/newsletter/october-2011