Hmmm. You are assuming that said "soujourn" into insanity leaves one with the ability to perceive the contrast when sanity returns. I KNOW it's not that simple. There's no "on" and "off" switch for sanity/insanity.
Insanity, I think, has to be the very worst of human ailments. One's SOUL is affected. We can only pray for those poor people and leave them to God's enduring love and mercy.
Um, GOD has that switch in His hands.
I think you consider insanity out of the control of even God. The bible testifies otherwise.
And if we study actual cases of insanity, we can see how they are frequently actually punctuated with lucidity. It is seldom all insanity all the time.
Can you wrap your head around the idea that God permitting this is a PUNISHMENT? But not an arbitrary punishment, but one tailored to teaching a soul.