The song features Maxi Jazz rapping from the point of view of an insomniac while he struggles to sleep ("I toss and I turn without cease, like a curse, open my eyes and rise like yeast/At least a couple of weeks since I last slept, kept takin' sleepers, but now I keep myself pepped").

The subject is resonant with fans of dance music, as stimulant use is common in club/rave culture, and insomnia is a common side effect - in a 2020 interview, Maxi Jazz acknowledged how it struck a chord with clubbers: "Suddenly the song was being played to crowds who had arguably taken 50 quid’s worth of high-powered drugs and weren’t thinking of getting much sleep for days...

[3] The insomniac is also rather destitute ("Make my way to the refrigerator/One dry potato inside, no lie, not even bread, jam, when the light above my head went bam...").

Although he was not an insomniac, Maxi drew on personal experience for the lyrics: he had recently suffered a painful dental abscess which had kept him awake at night.

Lines about the light going out and picking up a pen in darkness were based on the prepayment electricity meter in his home, which would cut out when credit ran out, forcing him to write by candlelight.

Maxi Jazz changed the opening line from "I only smoke weed when I need to" to "Deep in the bosom of the gentle night" due to pressure from MTV.

After the song gained popularity in continental Europe, Pete Tong campaigned for a re-release: Cheeky/Champion chose to hold back the re-issue so it arrived in shops on the same day as the Spice Girls' "Say You'll Be There", so it would be placed in racks alongside it.

Justin Chadwick from Albumism described the song as a "frenetic yet melodic ode to late night restlessness and sleep-deprived reveries", adding it as "phenomenal".

[6] Larry Flick from Billboard wrote, "This single serves as a fine peek into the project, giving listeners a taste of urgent dance rhythms, a complex and infectious pop melody, and vocals that are notches above the typical vamps heard on club-originated records.

"[7] Complex said that Faithless' "Insomnia" "spoke to a number of ravers out there who lived for the night/weekend and, sadly, the drugs that kept them partying to the break of dawn (and beyond).

"[9] Tim Jeffery from Music Week's RM Dance Update rated it four out of five, writing, "Following very much in the style of its predecessor with all the Rollo production hallmarks including the piercing organ and synth riffs and a bouncy bassline.

As with the debut, there's also the half speed section in the middle to incorporate the rap and vocals which aren't as instant as 'Salva Mea' but grow on you.

Outside Europe, the single reached the top spot on the RPM Dance/Urban chart in Canada and the Billboard Dance Club Songs in the United States.

[18] In 2017, Billboard ranked "Insomnia" number 20 in their list of "The 100 Greatest Pop Songs of 1997", naming it "a towering house opus wrapped around a late night's restlessness, turning the attempt to shed consciousness into an epic struggle, with as much internal conflict as the withdrawal scenes from Trainspotting.

"[19] In 2020, Mixmag featured it in their "The Biggest Drops in Dance Music", writing, "Maxi Jazz's spoken words about struggling to kip - alongside a heartbeat build-up - are deeply ingrained in worldwide consciousness, as are the piercing, relentless synth stabs that burst into the tune a few minutes in.