Written by Thomas "Orup" Eriksson and produced by Anders Hansson, "Delirium" is a disco and power pop song with synthesizer and guitar instrumentation and schlager influences.

[2] 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.

[17] The Länstidningen Östersund critic interpreted its lyrics as "completely mad", as if Philipsson was wearing a straitjacket while singing,[15] and Per Bjurman of Aftonbladet described them as humorous and ironic.

Jonas Fahlman of Norran named it one of the best tracks on Det gör ont,[18] and Håkan Pettersson of Nerikes Allehanda felt it represented Philipsson at her best and called it "perfect".

[19] Per Bjurman of Aftonbladet opined that the song may not be fully as catchy as "Det gör ont", but nonetheless a good mixture of classic schlager and modern pop.

[20] Anders Nunstedt of Expressen felt its "frisky" schlager chorus could have a chance of winning Melodifestivalen, and noted the production as "very simple" and radio-friendly.

[15] Similarly, Åsa Johansson of Falu Kuriren called it a catchy pop song,[22] while Micke Holmström of Norrköpings Tidningar characterized it as "cheeky" and "cool".

[23] Piteå-Tidningen critic Anders Sandlund was less enthusiastic and regarded the single as "strenuous" and named it the worst track on Det gör ont.

The song was Philipsson's third consecutive top-five entry of 2004 on the chart after "Det gör ont" and its English-language version "It Hurts".