You must read Why Is God Somewhat Stingy? first to be able to understand this article; especially, the concept of pardoxical drama. You may also read Why Does God Sometimes Make Our Faith Pointless? for some additional insight. Note that God does not really sometimes send unbearable torment.
Now, why does God sometimes send unbearable torment? First, the unbearability is unconsciously unreal, which is proven by the fact that we do not lose control of ourselves. So, why does God send the experience?
So that we will engage in the paradoxical drama of subordinating everything else in our lives to the work of eliminating the unbearable torment; that is, so that we put the elimination of the unbearable torment before every other task and responsibility.