I actually received an e-mail that asked me a question about which I can blather endlessly, in theory. One must understand that I have not reached these exalted heights and so all that I say is a synthesis of others.
"I've heard of two dark nights--dark night of the soul and dark night of the senses. The latter I take to be a kind of depression or unhappiness, the former the true unitive dark night. Any clarification?" (This is a gross paraphrase.)
Okay--let me talk about St. John of the Cross's scheme of spiritual growth in the via negativa. The way he sees development in prayer is through two DIFFERENT dark nights. The first of these two is called "the dark night of the senses." It consists of two parts, as does the latter. The first of these parts is the active, the second passive. In the dark night of the senses we enter into a deliberate attempt not to gratify the appetites. In olden days we would say that we would practice "custody of the eyes." But in the case of this dark night, we do not seek to gratify the senses--we deprive ourselves, as a matter of discipline and out of love of the Lord of those things we strongly desire. This is more than asceticism--it is a deliberate attempt to break the chains of desire that hold us away from God. If we love any creature inordinately, we cannot love God as He deserves. With this practice we enter into the dark night. In God's good time, as He sees fit, we may enter the passive night of the senses, in which God completes the purgation begun by our own effort and perfects it.
The second dark night is called the dark night of the spirit, and it too has a passive and an active phase. The second night focuses more on the spiritual faculties--intellect, memory, and the will, not the senses. I have yet to fully understand this, as I am slowly moving through the Ascent of Mount Carmel and Dark Night of the Soul. If you'd care to read more about this from someone far more knowledgeable than I, look here. Mr. Doohan does a wonderful job of explaining what may seem like abstruse doctrine in very comprehensible terms.
I'm still working--largely unsuccessfully--on the active night of the senses. But I have great hope that God will see fit to aid me in His time and in His way.