The speaker describes pain as an ocean moving through the body. It begins in the chest, spreads down the arms and legs, and crashes against the heart, lungs, bones and soul. At first the feeling is oddly welcome. The waves wear the pain down into numbness, and that numbness feels calm, even "amazing."
Then the poem shifts. It's 3 in the morning, tears are pouring, and the speaker realizes the pain has stopped feeling like pain at all. The questions at the end are uneasy and a little desperate: when did pain turn into pleasure, and why can't the speaker fix their broken pieces? The last line, with its grammar slip ("did i left"), reads like someone too tired or shaken to be polished, and it admits that the ocean has taken over the beach. The mood is quiet and heavy, soothing on the surface but frightening underneath, because the relief the speaker found has started to feel like losing control.