Psalm 88:5 (ESV)

5 like one set loose among the dead, like the slain that lie in the grave, like those whom you remember no more, for they are cut off from your hand.

Now, the author names the very worst thing rooted in his mind, eating him up inside. He feels that God does not think of him anymore. The Lord has pulled his hands off him. He let him go. (Compare with I had said in my alarm, I am cut off from your sight, Psalm 31:22a). And that is why I am a nameless corpse that no one looks at. I look like a fallen soldier who is carelessly thrown into a mass grave.