Songfacts®:

• The punkiest track Halsey has released to date, this song finds the empowered singer warning her man she's now ready to embrace her bad side.
  
  I'm no sweet dream, but I'm a hell of a night
  
  During Halsey's first two albums, Badlands and Hopeless Fountain Kingdom, she documented some of the hardships she's had to endure in her life. Now, in response to these trials and tribulations she will no longer play the victim. Instead the emboldened singer is ready to preempt any adversity by taking on the role of the aggressor.
• Halsey penned the angsty song with Benny Blanco, Cashmere Cat and Happy Perez. Halsey previously collaborated with the three other writers on Blanco's hit tune "Eastside."
• The music video, directed by Hannah Lux Davis, features cameos from Cara Delevingne, Suki Waterhouse and Debbie Harry.
  
  The clip features Halsey embodying various different personas, including a punk rocker, housewife, dominatrix and a glamorous model.
  
  "She really wanted to show how multifaceted women are," Lux Davis told MTV News. "We could be fighting in the street for sport and we could be in lingerie, really sexy and feminine and clean. That was the biggest thing that she wanted to say - just showcasing all different sides of what a woman is."
• Halsey performed "Nightmare" for the first time onstage on May 20, 2018 during a free show for fans at the Minneapolis Armory in Minnesota.
• Speaking on the Elvis Duran and the Z100 Morning Show, Halsey said the song was inspired by thinking about the way her experiences relate to her fans.
  
  "One of the things that a lot of myself, and a lot of my young female fans of mine have, is the experience of when someone is telling you to smile," she explained. "At some point, some man will look at you say, 'Ay, why don't you smile? You're so frigid. She would be so much nicer if she smiled. What a pretty face, you should just smile.' And you're like, 'I don't want to!'"
  
  "It you don't, then the narrative about you becomes, 'Oh that girls such a nightmare. She's so difficult, she's such a nightmare,'" Halsey continued. "I used to not like that, and I was like, 'Oh gosh, I don't want anyone to think I'm a nightmare. I don't want people to think I'm mean or rude.' So I found myself in situations smiling when I didn't want to smile or being nice to people who probably didn't deserve it. Not anymore, I'd rather be a nightmare than a bunch of jerks get away with forcing me into some kind of complacency, or some kind of convenience or positivity because they want to see it. It's for their own entertainment, and it makes them more comfortable. It doesn't matter if you're a famous person, or any person we can all relate to that experience."
• Speaking in an August 2019 Q&A with author/journalist Lizzy Goodman, Halsey said that female rage was a topic that was on her mind when she wrote the song. "I'm interested in female everything right now…I went from only wanting to hang out with boys to 'I love women, they're awesome.' I've grown out of my internalized misogyny."
• Halsey decided to make "Nightmare" a one-off single rather then recording similar dark tracks for Manic. The singer, who has been open about her struggles with bipolar disorder, said having to perform them would be detrimental to her mental health.
  
  Halsey also felt she'd vented all her frustrations in "Nightmare." "I couldn't think of anything to say because I wasn't mad anymore," she explained to the UK newspaper The Sun. "That was a lot I had to vent with 'Nightmare,' and I did it and then I had nothing else to do to draw from. Once I made peace, I was done with the anger."
• This song features in the Netflix TV drama series Tiny Pretty Things. It plays over the final scenes of episode 3 ("Class Act").
• The song's original demo featured an extensive interpolation of Tatu's "All The Things She Said." Halsey's boyfriend at the time, rapper G-Eazy, removed the sample.