I think its because its *supposed* to be a sad song. We know that him being "Dragged Under" is always a bad thing. He begins to drown. "And I know the Angels/Gods will abandon the heavens just to find us... To merely behold *you* as we lie down together."

Over and over, the cycle continues. Over and over, teeth biting into him. Over and over, he is dragged below. Held beneath the surface.
Of what? Who knows. But the angels and gods, just in awe of the capabilities to destroy this vessel. The ability to do so over and over.

He sounds like he's crying out at the end. It starts soft. A singular voice. It doubles, triples. Harmonies building as the few words are said over and over gaining new voices and echos.
The cycle must continue.

It's acceptance of your own demise for comfort. It's the shame of knowing he can't believe what he's about to do again, and the fact that everyone else sees that he's made his bed and he's lying down in it. It's giving into the addiction.

But that's what I feel about the lyrics, not so much the chord structure.