Call it Glastonbury for pretentious people. This weekend, Tate Modern hosted a performance of Vexations by the French composer Erik Satie, accompanied by Andy Warhol's film, Sleep, to mark the 20th anniversary of Warhol's death.

Vexations consists of two lines of dreamy piano plinkery lasting about a minute. But Satie - the wag - instructed players to repeat it 840 times so it lasts about 18 hours and 40 minutes. It's been labelled a minimalist masterpiece, the first techno tune, a torturous ordeal and a Zen joke.

Warhol loved it and used it as the soundtrack to Sleep (1963) - five hours of looped footage of his naked, sleeping lover John Giorno.

Being slightly pretentious, I was ready to love it too. When avant-garde composer John Cage first played it - using ten pianists in relay - it apparently offered blissful insights into the universe. I relished the challenge, and it amused me, too, to waste my time so wilfully in this frenetic city. Somehow I persuaded my friend Seb to join me.

We met in the Turbine Hall at 8pm on Sunday, just as Joshua Rifkin, the first of the Tate's ten pianists, began the tricksy melody. The place was surprisingly full. One couple brought a baby. We were woefully underprepared, having little more than a bit of bedding.

The first hour was tough. I was hungover and in a state of irritable melancholy; Seb, who had thought the jape would last 12 hours, was adjusting to the fact that he would lose his Bank Holiday Monday. John Giorno's hairy bum on the big screen provided little distraction. We texted our girlfriends. We adjusted our cushions. We began an intimate acquaintance with the Turbine Hall's ceiling.

After a nap, all was refreshed (the subject's the same, your perceptions change: a valuable lesson). The music became soothing, occasionally hilarious. Everything, in fact, but boring. We were reluctant to leave for loo-breaks; returning was a great comfort. "What did I miss?" Seb wondered at one point. "Eternity," I said. We played many games of chess (I lost them all, but it felt profound).

At midnight we had a crisis. The Tate café forbade us wine. "No late license," said the manager. "Do you think Warhol had to contend with this in '63?!" I demanded.

Sensitive to variation, we developed favourite performers: Michael Nyman was too aggressive; we admired the delicacy of Andrea Fan. At 3am we settled down to disturbed sleep. I dreamed of Vexations and awoke each hour having slithered three feet down the impossibly hard, sloping floor.

Monday's dawn renewed our spirits. Regular gallery-goers with excitable children arrived. The 20 or so survivors exchanged solemn nods and chatted to the musicians, exhausted from the feat of concentration. One of them, Tania Chen, had tried to sleep in the performers' lounge, but was prevented by Nyman's slumbering noises: "He even snores like a minimalist - no variation", she complained.

Why we had done it we were still unsure, but we had done it, and that seemed important. Our girlfriends arrived to congratulate us. As Gavin Bryars played the last note at 2.40pm, I couldn't resist shouting "Encore!"

(This is a column that appeared in the paper today. Will offer less formalised thoughts on this strange event when I get a sec!)