God has had pity on me, he has changed my bitterness into sweetness, he has applied a balm of joy on the injury of my heart, so that, even as it is still suffering, it does not cease to experience a profound happiness.
Little Brother Marcel Văn CSsR (1928–1959)
Christian contemplation thrown into the muddy highways of the world : encouragement : experiences : resources
Contemplative in the Mud 
What was the nature of his suffering, do you know? Was it a spiritual ‘dark night’, or was it life circumstances or illness? I wonder if God can use each in the same way.
Hmm, I would answer in this way…
Life circumstances and illness can condition what someone like John of the Cross calls a dark night – although the nugget of spiritual progress has to be there, too, for it to be a real dark night. John himself actually points this out, though a lot of people explaining his teaching nowadays don’t notice John’s quick aside on the subject. (Others such as Alphonsus Liguori, Catherine of Siena, and John of Avila are more insistent and perhaps clearer on the subject.)
Any suffering can be a participation in the Cross, but it depends on where we are in virtue and prayer, what we are able (or asked) to see as God’s providence, etc.
For little Van, I think it was this kind of providentially conditioned dark night. If it were not a dark night, he could not change sadness/suffering into joy by the Cross. But Van’s way of life seems to leave one to believe that it was in providence, not only mental prayer, that his dark night was lived.