What is nightmare dressed like a daydream meaning?

"Nightmare dressed like a daydream" is a lyric from Taylor Swift's hit song "Blank Space". The phrase is a metaphor, indicating that the situation the speaker is in seems beautiful and perfect on the surface, but is actually filled with darkness and chaos. It suggests that things are not as they seem and that the speaker is in a dangerous situation despite appearances. The phrase has been interpreted in various ways, but its central meaning is usually associated with the idea of a false or misleading reality.