Four short lines carry a lot of quiet strain. The speaker is physically unwell, with a sore stomach and a aching throat, and close to tears. The twist comes in the last line: crying has to wait until the next day. We aren't told why, but the poem suggests a situation where showing weakness isn't possible right now, perhaps because of other people's expectations or simply the need to keep going.
The title, "Unhealthy Behaviour," changes how we read the symptoms. The stomachache and tight throat feel like the body's response to swallowed emotion, and the title hints that suppressing feelings like this isn't good for us. The plain, simple wording and the lack of any explanation make the mood tense and tired. Nothing is released, and the poem ends on the delay itself. That unresolved ending leaves a sense of loneliness and pressure, the feeling of carrying something heavy while looking fine.