I have always found it a comfort that Night Prayer in the Liturgy of the Hours is primarily made up of psalms for the sick, the lonely, and the distressed.  The Church includes Ps 88 for Friday night, a psalm Derek Kidner refers to in these words: “There is no sadder prayer in the psalter.”  It is a psalm I have prayed myself in true earnest.  It begins: “O Lord, my God, I call for help by day; I cry out in the night before thee. . . . For my soul is full of troubles, and my life draws near to Sheol.  I am reckoned among those who go down to the Pit; I am a man who has no strength. . .” and ends with this verse, “You have turned my friends and neighbors against me, no darkness is my one companion left.” (JB) 
      I appreciate the honesty of the pray-er of this psalm, for we all have days or seasons during which we can identify with him.  What is most important is that it is a prayer.  It is always better to pray out of the honesty of our hearts than to feel that we cannot pray, that what we have to say is too sad or anguished or distressing and thus not acceptable to our God.  What father would not want to hear the anguish of his child? 
      Some final comments from Kidner:

With darkness as its final word, what is the role of this psalm in Scripture?  For the beginning of an answer we may note, first, its witness to the possibility of unrelieved suffering as a believer’s earthly lot.  The happy ending of most psalms of this kind is seen to be a bonus, not a due; its withholding is not a proof of either God’s displeasure or His defeat.  Secondly, the psalm adds its voice to the ‘groaning in travail’ which forbids us to accept the present order as final.  It is a sharp reminder that ‘we wait for adoption as sons, the redemption of our bodies’ (Rom 8.22f).  Thirdly, the author, like Job, does not give up.  He completes his prayer, still in the dark and totally unrewarded.

Kidner goes on to point out that, in fact, the author’s rejection was only apparent:

This supposedly God-forsaken author seems to have been one of the pioneers of the singing guilds set up by David, to which we owe the Korahite psalms (42-49; 84f.; 87f.), one of the richest veins in the Psalter.  Burdened and despondent as we was, his existence was far from pointless.  If it was a living death, in God’s hands it was to bear much fruit.

Let your anguish be a prayer.  In His hands it will bear much fruit.