Poena damni
The poena damni, or pain of loss, consists in the loss of the beatific vision and in so complete a separation of all the powers of the soul from God that it cannot find in Him even the least peace and rest. It is accompanied by the loss of all supernatural gifts, e.g. the loss of faith. The characters impressed by the sacraments alone remain to the greater confusion of the bearer. The pain of loss is not the mere absence of superior bliss, but it is also a most intense positive pain. The utter void of the soul made for the enjoyment of infinite truth and infinite goodness causes the reprobate immeasurable anguish. Their consciousness that God, on Whom they entirely depend, is their enemy forever is overwhelming. Their consciousness of having by their own deliberate folly forfeited the highest blessings for transitory and delusive pleasures humiliates and depresses them beyond measure. The desire for happiness inherent in their very nature, wholly unsatisfied and no longer able to find any compensation for the loss of God in delusive pleasure, renders them utterly miserable. Moreover, they are well aware that God is infinitely happy, and hence their hatred and their impotent desire to injure Him fills them with extreme bitterness. And the same is true with regard to their hatred of all the friends of God who enjoy the bliss of heaven. The pain of loss is the very core of eternal punishment. If the damned beheld God face to face, hell itself, notwithstanding its fire, would be a kind of heaven. Had they but some union with God even if not precisely the union of the beatific vision, hell would no longer be hell, but a kind of purgatory. And yet the pain of loss is but the natural consequence of that aversion from God which lies in the nature of every mortal sin.
http://www.newadvent.org/cathen/07207a.htm