Jewish Interior designer Jérôme Elkaïm was tired of standing in the crowded concert hall. He'd been on his feet watching the support act and the band he'd come to see, the Eagles of Death Metal, were taking a while to set up.

He decided to go to the bar for a drink and then head upstairs - a decision that saved his life.

From the balcony, he first heard the gunfire, then the sounds of panic, and he watched as the band suddenly fled the stage.

"I didn't want to believe it. It was unimaginable. When I heard the panicked screams, that's when I looked to see what was happening," said Mr Elkaïm, 33.

"People were rushing towards the front of the room, as if they were trying to get away from something behind them. I looked over the balcony and I saw people being murdered, one by one, in front of my eyes. I saw at least 10 dead bodies lying on the ground, and lots of blood. And there were people who were lying down. It was hard to tell who was dead and who wasn't.

"I saw people crawling towards the stage. They were crawling over each other to escape.

"When I saw that I put my arm around my friend and we crawled behind the seats silently until we came to an airlock corridor. There, we discovered a skylight that led on to the roof.

"There were around 60 or 70 of us. We decided the women should go first and we gave each other a leg up to get out. Then I found myself on the rooftop with my friend. We walked across it and entered an apartment. Once there, we were safe.

"I didn't panic. I had someone to look after, that helped me to look at things in a pragmatic, rational way.

"I didn't think about the murder I had seen, but about how to escape. I was scared but it didn't prevent me from being rational."

The group - around 70 of them - stayed in the apartment with the lights off for around two hours, listening to the repeated sound of gunfire.

As he sent text messages to friends to let them know he was safe, he heard the explosions as the gunmen detonated their suicide belts.

He decided not to contact his parents, because he thought they would be asleep.

A short time after the police raid, officers came to the apartment and searched everyone for explosives.

When he was eventually able to leave, he and his friend went to his girlfriend's home on rue de Charonne, close to La Belle Equipe café, which had been attacked earlier that night.

His girlfriend, a doctor, gave him pills to help him sleep.

He lives in the Paris suburb of Montreuil and grew up on Boulevard Voltaire in the 11th arrondissement, just down the road from the Bataclan. His parents now live in the 20th and his father, also a doctor, is a regular attendee of the synagogue Fondation Rothschild.

Today Mr Elkaïm remains quite collected. Asked how he feels, he said: "I don't know. I get the impression I'm less shocked than everyone, I feel like because I saw the attack, it was not as bad as watching it on the TV.

"I don't feel bad, or good, just weird really. I'm okay, but maybe tomorrow I won't feel okay.

"Maybe it's the kind of thing that comes back to you."