Nightmare begins with a trap: the speaker expected a dream and landed somewhere much darker. From there the poem piles up the pressure. Their head spins, their thoughts feel empty, and all they can hear is their own heartbeat and voices chipping away at their confidence. Sadness pushes them into a corner with nowhere to go.
What makes the poem interesting is how the speaker responds to help. Hands reach out, offering "some kind of salvation," but the speaker refuses it, and the shift from "I can't" to "I won't" sounds like a hardening of will. The ending then draws a careful line: "I feel alone, / but I'm not lonely." The speaker admits the nightmare is a solitary one, yet claims ownership of it, saying they have written their own life and will live in it.
The mood is anxious and heavy at first, then stubborn and defiant, with a hint of resignation in the final line.