In that sentence, “fugue state” refers to a mental state where the character feels detached from reality and almost unaware of themselves, like they’re slipping into a kind of trance or dreamlike state.
It’s not being used in the strict psychological sense (where a fugue state involves dissociative amnesia and wandering). Instead, it’s more figurative: the repetitive sound of the rain (“patter on his hood”) acts like white noise, and it’s lulling him into a calm, thoughtless state—“free from the churn of his thoughts.”
The parenthetical — “was that the phrase?” — shows he’s not entirely sure if he’s using the term correctly, which adds to the sense that his mind is drifting or slipping out of focus.
