What are the cords of Sheol?

After returning to the throne in Israel, and defeating the Philistines yet again in the story, David sings a song of deliverance to the Lord. When referring to his iniquities, David sings:

“For the waves of death encompassed me,
the torrents of destruction assailed me;
the cords of Sheol entangled me;
the snares of death confronted me.”

-2 Samuel 22:5-6

What or who or where is Sheol? What does it mean to be entangled by its cords? As we have learned of the Hebrew poetry, it uses parallelism to express that ideas “are nearly synonymous in meaning and are of equal force” (Parallelism in Poetry). From this we can assume that Sheol is associated with a feeling of dread, like death and destruction. It is used this same way at least twice, in Psalms 18:5 and 116:3. Here it is seen as something that could ensnare you. 

The King James Version of the Bible translates Sheol to Hell in some instances, but not in all. There is evidence that Sheol could be a place like we think of as Hell, or Hades, or wherever bad people go when they die because “They don't go to heaven where the angels fly” like Meat Puppets put it.

Here are some ways it is similar to our perception of Hell:

1. It is a pit, possibly even underneath the surface of the earth (Deuteronomy 32:22, Job 11:7-8, Psalm 88:3-6, Isaiah 14:4-15).
2. Only the dead go there, especially the wicked (Genesis 44:29-31, Job 7:9, Job 21:7-16, Psalm 31:17, Proverbs 9:17-18, Isaiah 57:8-9).
3. It is like an unyielding fire (Song of Solomon 8:6).
4. It is synonymous with death and darkness (Isaiah 28:15-18, Job 17:13, Habakkuk 2:5).

Anyone not of Israel was doomed to this horrible place. In the New Testament, we can see the effects of this same thought process from when the Hebrew scriptures were translated into Greek and the word “Hades” is used as a substitute for Sheol. In this sense, Hades is not only the underworld, place of the dead, but also the personification of the evil it represents (The Westminster Theological Wordbook of the Bible). 

In some sense, though, it is believed to be the resting place of the dead, whether righteous or wicked (Ecclesiastes 9:2-10). This excerpt from the book of Ecclesiastes seems to me to have a certain sense of “carpe diem” to it. Like Robert Herrick's “To the Virgins, to Make Much of Time” and Andrew Marvell's “To His Coy Mistress,” it even stresses the importance of sharing love with someone. The verses advise in this manner because, according to the writer, no matter what you do, you are going to Sheol.

I personally think that Sheol was at once an actual place, possibly like a graveyard; and that over time, as an afterlife in the absence of the protagonist, God, was constantly compared to death (continually) that the meaning of the name of the place became synonymous with the resting place of a nonbeliever.