As for you, O Lord, you will not restrain your mercy from me; your steadfast love and your faithfulness will ever preserve me! For evils have encompassed me beyond number; my iniquities have overtaken me, and I cannot see; they are more than the hairs of my head; my heart fails me. -Psalm 40:11–12
Back in Psalm 38:4, a similar experience is treated in which the iniquities of the Psalmist overwhelm him also. He is only able to speak of his plight because of the mercy of the Lord to preserve him.
Note the powerful metaphors he uses to explore the great heaviness he feels from his sin: encompassed by evils innumerable, overtaken, blinded, and discouraged (dis + cour = not having heart]).
This reminds us that sin is a heavy burden to bear and unconfessed sin compounds its weight. See 1 John 1:9 & 2:1.