Ether Frolics, Shunt Vaults, London

This is a medical nightmare, with wonderful dreamy bits. The place looks clinical: a small raked auditorium surrounded by white curtains. A young doctor stands before us, kitted up in surgical rubber boots, telling us in soothing tones: "This will take about half an hour and afterwards you won't remember a thing." However, things are getting weird. He's wearing a dressing gown and an echo has crept into his voice. Still deadpan, he suggests that we might want to kiss him later, but he's just going to lead us now into the darkness, the blackness, the horror, the death. Then the lights go out for what seems like an eternity.

Ether Frolics is stunning in two senses of the word, being an impressionistic piece about anaesthesia which is simultaneously thrilling - a paradox, in fact, in tune with the effects of nitrous oxide and ether. The programme notes back that up with splendid, first-hand historic accounts by blissful guinea pigs including Sir Humphry Davy and the poet Robert Southey who, on inhaling laughing gas, saw streams of dazzling, magnified images and experienced tingling in every toe and fingertip.

Jointly devised by the experimental collectives Sound&Fury and Shunt - with backing from the Wellcome Trust - this is a macabre, droll and magical cabaret-cum-hallucination. It is as if you have been "put under" in an operating theatre but your senses seem twice as alert as normal.

Primarily, it's the darkness that does the trick. In the pitch black, the smell of death alarmingly fills your nostrils - the mouldering odour of Shunt's vast, dank vaults seeping through those flimsy curtains. Mark Espiner's staging - co-created with the acoustic and lighting experts Dan Jones and Simon Macer-Wright - is also brilliantly disorienting. Eerie sounds wash around you: a clanging of swing doors; an orchestra like a floating memory; hushed voices, electronic beeps and pulses - sometimes serene, sometimes manic as if the op is going horribly wrong. Meanwhile, as you stare into the void, faint falling stars start to rain slowly across your vision. Glowing triangles spin mesmerisingly out of nowhere. Three dazed gothic figures in black-tie are glimpsed, wedged on a tiny crimson stage, trying to operate on a parcel stuffed with newspaper. Later, a woman with a glass of milk is hauntingly glimpsed, doubled up in a mint-green chamber, trying to snap shut two boxes with panting heads inside. These visions fascinatingly blur doctors' and patients' troubled dreams.

A few scenes outstay their welcome and Tom Espiner can be an obtrusively self-conscious actor in these realms of the subconscious.

Still, David Rosenburg entertainingly conveys complete panic with tiny twitches and Hannah Ringham has bruised anger under her clowning. The special effects are transcendent and I remember every moment vividly.

Knock-out.

To Saturday, 020 7223 2223