Nightmare is a song by American singer Halsey. It was released as a single on May 17, 2019 and was sent to top 40 radio on May 21, 2019 through Capitol Records, but not included in any album until the release of If I Can’t Have Love, I Want Power (Extended). The song was written by Halsey along with its producers Benny Blanco, Cashmere Cat, and Happy Perez. The music video, directed by Hannah Lux Davis, accompanied its release the same day.
The song has received positive reviews. Billboard magazine said the song is musically "unorthodox" containing "stylistic curveballs" and "killer lines" that "exalt autonomy, sexual freedom and self-acceptance". The line "I've been polite, but I won't be caught dead / Letting a man tell me what I should do in my bed" was noted as a "barbed assault on patriarchal expectation" by Billboard and "a necessary gesture of rage and empowerment" by Rolling Stone. Billboard named it the 17th best song of 2019. .