His groaning represents the pain or distress that he feels. Alternate translation: "I am very tired because of my pain" (See: [[rc://en/ta/man/jit/figs-metonymy]])
Possible meanings are 1) these are two words for the same thing or 2) the "couch" is the main cushion on the bed or 3) the "bed" is where he sleeps at night and the "couch" is another item of furniture.