Dream
It's the 21st century so torture methods need to have some standards. One technique that we used to use involved enabling the subject to have the best non-lucid dreams imaginable. Of course we would then rip them out of their dreams and bring them back to reality.
The pain of reality has proven more than strong enough to cause subjects to directly (attempt to) commit suicide.
In the end, a dream is just a dream and not reality. That realization can definitely also cause insanity.
For all you know, your current life is just a dream.