Someone asks the speaker what's on their mind, and the honest answer is a nagging, stressful feeling that keeps creeping in and won't leave. The poem is short and plain, and that suits it: the speaker isn't dressing up their worry, just naming it.
The key tension is between what the speaker says and what they actually feel. They keep telling themselves, and probably others, that they're fine, but the feeling sticks around anyway. The repetition of "I say" against "it doesn't go away" shows how little the words help. By the end, the speaker admits that lying to themselves might make time pass, but it's bad for their mind. The blunt "sure as hell" gives that line a tired, frustrated edge.
The mood is uneasy and weary, but also quietly honest. The speaker hasn't solved anything, yet admitting that pretending doesn't work feels like a small first step toward facing the stress instead of hiding it.