See http://www.ccel.org/ccel/john_cross/dark_night.txt

Hard to read...

Very important text that describes a phase all of us believers are going through of great skepticism emerging from deep inside and consequently all structures previously built collapse.

It helps being less identified with this terrible state and letting it be until it vanishes and a great joy remains.

Those whose occupation is religious undergo the worse suffering of the dark night of the soul because it influences the center of their doing.

Strange as it may sound, Mother Theresa is known to experience this phase for so many years without having any resort in that text.

See also in http://www.gurusfeet.com/forum/i-039-m-skeptical-spirtualist-what-should... and http://www.gurusfeet.com/category/spiritual-tags/skepticism.

I like the explanation for Dark Night of the Soul in the first link:

We all have our substratum of sanskaras (conditioning / imprinted patterns) of disbelief, especially those of us who were raised in secular environments. And even those who grew up in truly-spiritual families (these are very rare) have their minds (whose nature is rational and thus skeptical) cultivating new skeptical sanskaras, partly as a mechanism of survival.

It is said that surprisingly enough the skeptical conditioning surfaces in full power when you are established enough on the path, paradoxically when your connectedness with the beyond is strong enough because at that point your consciousness is pure enough to contain these subconscious doubts.

"The dark night of the soul" is painful especially because at that point it is the last thing you expect to happen.