The smell of a firework or the sight of blood can take Michael O'Connor back to the night when 89 people lost their lives in the Bataclan terror attack in Paris.
"I have lots of images from that evening - pretty disgusting images in my head which can be quite hard to remove," he said.
Michael, 31, was hailed a hero after covering his French girlfriend Sara Badel with his body to protect her from three gunmen firing in the concert hall. They both survived.
But a year on from the atrocity, he has told the BBC how the horror has left him a different person.
"Sometimes I can find myself, over something really small, completely losing my temper - and that's not who I am," he said.
"Or being incredibly sad - and that's not the kind of person I was before. Before, I was a fairly happy-go-lucky person and enjoyed life, I guess.
"That's not to say I don't enjoy life now, because I'm incredibly thankful I'm alive - and I intend to appreciate every second of it.
"But yeah, I guess I'm a changed person, a changed man a little bit."
The chef, who is originally from South Shields, South Tyneside, said he had experienced feelings of happiness and depression following the attack.
He added: "Obviously, time is a great healer - and a year isn't a long time in the great scheme of things.
"So as the weeks, months, years pass I'll get back to the person I was.
"I'm not far off, I hope."
Michael had been dancing near the stage with Sara, 28, when the gunmen entered the Bataclan concert hall and began firing at the crowd.
It was part of a simultaneous attack across Paris by terrorists who also hit a major stadium, restaurant and bars - leaving 130 people dead and hundreds wounded.
The couple managed to escape physically unharmed but the mental scars are still evident a year on.
Michael said the first anniversary of the Paris attacks was causing him to have flashbacks.
He said: "It can be a smell, or a sound.
"If I get a whiff of fireworks, that sulphury smell can take you back there.
"Working in a kitchen - seeing blood splattering in the ground - can take you back."
Sara, a school teacher, said she had seen her boyfriend wake up as many as 70 times in one night with terror, and is concerned for his long-term mental health.
"He would fall asleep and wake up shocked, then fall asleep for three or four minutes, then wake up again. He thought that someone was chasing him," she added.
"He keeps saying he's fine and he's OK and it's OK for him to come off professional help, but it's not.
"I live with him and I see it, and he needs some help."
The couple, who met on a night out in Newcastle while Sara was working in a nearby primary school, live in Lyon.
They were visiting Paris for the first time when they were caught up in the attacks.
Michael admits their relationship has been tested by the horror they shared.
He said: "Although we went through the same experience, we experienced it differently.
"In one moment Sara might want to talk about it and I won't and vice versa - and that's very hard.
"At the same time, we survived something together so it's a paradox, I suppose. It can bring you together and push you apart.
"It's been hard but it's also worth it. I wouldn't change her for anything."
After escaping the Bataclan, the couple returned home and were visited by family and friends.
Michael said in the immediate aftermath he could not sit down, and forgot to eat and sleep because it didn't "seem important at that point".
He said: "Eventually you go out. I must admit I drank a lot, I ate a lot, I enjoyed myself and enjoyed being alive.
"Then suddenly you feel guilty that you're there and guilty you're enjoying yourself."
Sara added: "It's like grieving for a person who you love, who has just died, but with terror on top of it.
"You've got this feeling of deep sadness and emptiness and at the same time this feeling of terror."
'Gradually it gets better'
In an attempt to put the attack behind them, the couple booked a month's holiday to Thailand.
Michael said he has tried to replace the memories of that night with happier ones.
He added: "Gradually, it gets better and you start to see your friends and family and go places you've never been before - and you try and replace some of those things you've seen with good images.
"I've met so many good people, it reminds you the world isn't an evil place."
The full interview with Michael will be broadcast on BBC Radio 5 live's Stephen Nolan programme at 10pm on Sunday 13th November.