The poem starts out light, almost like a quiz: what are our worst fears? Spiders, heights, the dark. But the speaker quickly turns the question around. The real fears are quieter ones, like failing, going unloved, being lonely, or facing the unknown. "I do," the speaker admits, and guesses the reader does too.
The middle sections play with a comforting idea: fears are like nightmares, nightmares are like dreams, and they fade when you wake up. But the closing lines hint that this comfort is only "so it seems." The speaker says they once wished for dreams to come true without thinking that nightmares might come true as well. The short, blunt lines "no we didn't. i definitely didn't." sound honest and a little ashamed.
The mood moves from casual and almost playful to vulnerable and heavy. The final line, set alone, lands like a quiet shock: the fear is no longer imaginary, and waking up doesn't make it go away.