"Delirium" was written by Thomas "Orup" Eriksson for Lena Philipsson's studio album "Det gör ont en stund på natten men inget på dan" (2004). Philipsson enlisted Orup to write the entirety of the album's music and lyrics. The two started working on the record after she won Melodifestivalen 2004 with "Det gör ont", which advanced her to the Eurovision Song Contest 2004 in Istanbul, Turkey, where she finished fifth in the final. In an interview for "Aftonbladet", Philipsson described "Delirium" as a "contrast" to "Det gör ont" and lauded Orup's songwriting. She elaborated in a later interview, "I really like this one and I've listened to it a lot so I'm starting to get a little tired of it. I think it's so typical of Orup to come up with the title 'Delirium' ... I smiled the first time I heard it. First a song called 'Det gör ont' ('It Hurts') and then 'Delirium' – yes, what an album!" Orup also provided backing vocals on "Delirium".