The speaker wakes from sleep because a fly has landed on them, and the small, ordinary moment seems to open something up. The fly walks across "that ground" and then "this ground," which suggests it is crossing the speaker's own body. The repeated word "ground" makes the skin feel like a landscape, and the "silence" around the fly's walk makes the scene hushed and strangely intimate.
Then the tone turns. The speaker says they must "keep more distance / from my pleasures," as if enjoyment has a cost. The title, "Day tripper," hints at someone who only visits pleasure briefly, though the poem doesn't spell out the idea. What follows is physical: an ache "down down down / into the bone." The repeated "down" makes the feeling sink deeper with each word. The mood is quiet, wary, and a little sad. A lazy moment of rest becomes a reminder that what we enjoy can hurt us.