Welcome to the forum Michel =)
As you've probably figured out by now, our thesis is that when we spend long periods of time in meditation (prior to the stilling of the mind) it has the effect of bringing to the surface a large variety of uncomfortable, unhappy or contradictory memories, which have, until that time, existed in the unconscious mind. As these memories, pains, and incongruities get integrated into our conscious mind, we experience a large amount of turmoil, and this painful period is what is called the first "dark night of the soul."
However, after this experience is gone through, one gains the ability to access the 1st and 2nd jhanas (joy and relative silence), which become established both in meditation sessions, and, also, come to remain with you throughout the day.
Important, also, in developing these first two jhanas is the cultivation of vitarka (applied attention) and vicara (sustained attention).
Finally, if we become very adept as contemplatives, having remained with the still mind (the 2nd jhana) at many hours of the day, this can have the effect of provoking a -second- "dark night of the soul." In this experience, we again are transformed in a dramatic way, and come to reap the charisms, the later jhanas, and many other strange phenomena.