Psalm 88 ends in unresolved darkness: "darkness is my closest friend." No turn toward hope. No resolution. The psalm ends exactly where it began — in the pit, crying out, not yet answered. And it is in the Bible. God included this psalm in Scripture, which means unresolved darkness directed at him is not faithlessness. It is prayer. The person in crisis who can only cry out without hearing back is doing something Scripture explicitly validates.
Jeremiah 29:11 was written to people in Babylonian exile — people whose lives had been shattered and whose original futures were cancelled. God did not tell them their present circumstances were fine. He told them there were plans being held for them — tiqvah, a future and a hope — that had not been cancelled by what had happened. The darkness you are in is not the total picture of what exists for you.
Commentary is from a charismatic Protestant perspective, drawing on KJV text and public-domain sources including Spurgeon, Andrew Murray, and Matthew Henry.