I am utterly bowed down and prostrate;
(Psalm 38:6)

Psalm 38 shows us the burden (“my plague” vs.11) and effect (“I am spent and crushed” vs.8) of our sins, and teaches us how to ask (how to beg) for forgiveness.
Verses 18 and 6 of this Psalm form a vitally important, multi-part acknowledgment of sin:
1) I confess (with my lips)
2) I am sorry (in my heart)
3) I am utterly bowed down and prostrate (physically doing something about the sin)

Our sin is an offense against God, and we need to do something about it. Asking the LORD to forgive our sins is big (well it should be big). So what can we possibly do about our sins?  The writer of the Psalm is teaching us to humble ourselves, to bow down, to prostrate ourselves before the LORD and beg for forgiveness.