Decked out in pyjamas, slippers and eyemasks, the 20 strangers assembled at the Wellcome Collection on Saturday night did not look much like a traditional concert audience. The venue was equally unorthodox. Campbeds nestled between the reading room’s bookshelves, torturous surgical apparatus and displays of alchemist flasks as we waited for the clock to strike midnight and the beginning of renowned Anglo-German composer Max Richter’s latest experimental work, Sleep.

Described by Richter as a lullaby for our frenetic world, Sleep has been designed to soothe the listener into a gentle slumber, and at eight hours long is intended to last for a complete night’s rest. It was performed as the live audience – and those listening as the work was broadcast overnight on Radio 3 – went to sleep.

The piece, which features piano, strings, and vocals fused with gentle electronics, was composed in consultation with the American neurologist David Eagleman as a way for Richter to explore the effect music has on subconscious minds.

“For me, sleeping and music are both altered states; they are different ways of perceiving the world and relating to the world,” said Richter. “I feel like they are intuitively connected in some way – the lullaby tradition is globally universal, so this idea of sleeping to music is obviously something as a species we like doing.”

As Richter sat at his Grand Steinway piano surrounded by an ensemble of five musicians, a single soprano, synthesisers and stands holding hundreds of sheets of music , the audience nestled down in blue sleeping bags.

Offering a final piece of advice , Richter said the soporific undulations of piano and strings, soaring harmonies and low droning bass would be a “voyage of discovery”.

“The piece is to be slept through, it is a lullaby, but it is also an experiment in the way that music and consciousness can connect through this other state,” he said. “There are some things in this piece that I’ve been carrying around a long time.”

Sleep has never come easy to me. But as a silence cloaked the room and the soft piano chords began, followed by the deep melancholic vibrations of the cello, I was engulfed by sense of calm.

Actual sleep was sporadic. After finally drifting off two hours in, I woke almost every hour, sometimes to the haunting voice of a soprano, other times to deep ambient electronic vibrations.

Between the hours of 4 and 5am I sat up with a cup of herbal tea and just watched the violins. But when 8am came, and I awoke to the sound of applause, I felt like I’d spent my night in a deep, dreamless slumber.

Richter and the musicians had rehearsed the piece between 9pm and 4am to prepare themselves for the eight-hour musical odyssey, which earned them the Guinness world record for the longest piece of music ever broadcast live.

Speaking after the performance, Richter, looking triumphant and more than a little weary, said it has been an eye-opening experience.

“Some of the hours went by really quickly, and some of them really didn’t,” he said. “There was a 4am-5am dip where the exhaustion really kicks in and I was standing at the piano thinking: why did I write this again? But overall it was really interesting. The piece felt very different. As soon as you put a piece of music in front of a live audience it becomes more, because then it’s a conversation.

“I really enjoyed performing to a sleeping audience because again it makes the piece more than dots on a page. I’m obsessed with sleep, and to see the music have that effect on people, you feel like you’re in a privileged space. People felt relaxed enough, safe enough, to go to sleep.”

The consensus among my bleary-eyed companions was that while few of us had got very much sleep, none of us minded. Jenny Roditi, a composer, waxed lyrical about the impact the piece had on her dreams.

“I’ve had the most extraordinary time,” she said. “Particularly, the first two and half hours, I was half asleep but it was like I went inside my mind and I saw all these very delicate structures, like holograms and balloon-shape translucent bubbles.

“I’ve never experienced anything like it. The music was evoking these special spaces I think. I was half awake, half asleep most of the night. As a sound world, it was such an embarrassment of riches.”

Ina Hanisch, 34, who had travelled down from Edinburgh for the concert, said she hadn’t got to sleep till 5am but had woken at 8am feeling “completely relaxed”.

She said: “It was an amazing experience. I definitely preferred the live version, something about the atmosphere of being here maybe.

“I’ve got a history of insomnia, which was partly why I was so interested in this piece – and even though up stayed up most of the night, it was absolutely fantastic to just lie there and listen. I felt really in it at times, it completely absorbed you.”

• SLEEP is out now on Deutsche Grammophon