I tried floatation therapy, a crazy womb-like sensory deprivation technique that can be hallucinatory

LONDON - As I lay in the inky blackness, a strange noise began to rise. Scratching, rubbing, alien and unplaceable - the only sound in a cocoon of total silence. Where was it coming from? I darted my eyes around the darkness, trying to identify it, and it only intensified.

And then I realised: It was the sound of my eyes moving in their sockets.

In September, I got a chance to try out "floatation therapy." It's a far-out procedure that's part-physiotherapy, part-new age spirit journey, part-relaxation technique.

It's intended to cause extreme sensory deprivation: You lie in a closed pod in total darkness and silence, floating in water full of Epsom salts to aid buoyancy. It's kept at body temperature, meaning you can barely tell where the water ends and the air begins: You just float there alone, suspended in a silent, indeterminate darkness.

It's intensely relaxing, and without stimulation, your mind runs wild - meaning it can even be hallucinatory.

(Read on to see how I found it - but if you want a condensed version, there's also a video documenting my experiences here.)