Samatha Munns, 35, slipped from a stockroom stepladder and was speared by a metal spike. A high-powered jet of helium - enough to fill a large balloon - was released into her left thigh.

The accident happened in Buttercup Days, a toy shop she owns in Cheltenham, Gloucestershire. "I heard a hiss as I fell on top of it but I didn't realise what had happened until I saw the swelling. I looked down and saw my left thigh and side of my tummy were inflated like a balloon.

"I looked like I was five months pregnant. I thought I was going to die. I have heard it can be fatal if air gets into your veins."

A customer who came into the shop called an ambulance.

Doctors at Cheltenham General hospital consulted colleagues at Guy's hospital, London, about what to do. One plan was to insert 70 pins into her skin to deflate her body. They decided instead to allow her home and let the body absorb the gas.

Alison Moon, who treated Mrs Munns, said: "The x-rays of her thigh showed that it was about twice the size of her other thigh.

"There was a very black area on the x-ray which was the streaks of helium under the skin of her leg."

The "bubble" took a fortnight to deflate, having first travelled to her knee and up to her neck.

"I do accept it was a bit daft to climb up above the tank with a spike like that on it," Mrs Munns said.