The title suggests something has just ended, and the speaker seems left in a strange, deflated state. The first three lines read like a string of restless wishes. The speaker longs to "sink into a silver spoon", which is a small, shiny, almost comic place to disappear into. Then comes a wish to strike out "like a musket", something sudden and forceful, and then a wish to try "a cheap experiment with change". These impulses pull in different directions: hide, lash out, or gamble on something new.
The last two lines bring everything down to earth. The speaker has put off a meeting, and the reason is physical and unglamorous: "less trouble in my stomach." Anxiety, it seems, is showing up in the body.
The mood is nervous, tired, and a little darkly funny. Big images of violence and escape sit beside a very ordinary stomach ache, and the poem lets that contrast speak for itself. Judging by the title, "campaign" could mean war, work, or politics, but the poem never says.