Thunder keeps a speaker awake all night, and the poem captures how frightening that can feel. Loud booms come through the window, lights flicker, and the speaker lies shaking under the bedsheet. The short, broken lines work like quick breaths or a pounding pulse: "Heart racing," "Quivering beneath the sheet." They make us feel how hard it is to stay calm.
What stands out is how the fear grows. At first it is just noise, but then the speaker's mind begins "hallucinating worst," imagining the worst possible outcomes. Thoughts become scattered, and when the thunder returns, the speaker grips the pillow as if it were the only solid thing left. The final line, "Thought death was at my door," is the peak of that panic. It is dramatic, but it fits how a frightened mind can exaggerate in the dark.
The mood is tense, helpless, and claustrophobic. We stay in the bed with the speaker, with no relief or morning in sight, only the storm and the fear it stirs up.