Kim's poem is about the grip of a powerful craving, and the exhausting effort of not giving in to it. The poem never says what the urge is, and that vagueness lets the reader feel its force without a label attached. What we get is the physical side: something "eating at me from the inside," a churning stomach, bile working at the stomach walls. The speaker's body seems to be under attack.
The mood is tense, numb and worn down. The repeated line "the only thing I can do is wait it out" sounds like a mantra, but it also feels like a trap, since waiting is all there is. The ending is the unsettling part. "Or give in" hangs there each time, a constant temptation. The second stanza adds the image of rocking back and forth and being too numb to cry, which suggests a pain with no outlet. By returning to nearly the same lines at the end, the poem makes the struggle feel like a cycle that keeps starting over.