Kelly was one of the first TV reporters to arrive at the scene after Pan Am Flight 103 exploded mid-air, killing all 259 people aboard and 11 on the ground.
The presenter, then 29, said she witnessed the devastating aftermath of the disaster, which included dead bodies as she drove through the town.
However, despite seeing the death and destruction first hand she thought she had put the images behind her until 2018 when she suffered a breakdown.
“I was just doing my job. Nobody I loved was murdered – and they were murdered as far as I am concerned," she told Daily Telegraph of the tragedy, which saw Libyan Abdelbaset Ali Mohmed al-Megrahi convicted in 2001 of planting the bomb on the plane.
“For years, I always said, ‘I do not have the right to this, to have these feelings’,” says Kelly. “PTSD is not me, that’s for all the people who went through losing people or were living there at the time. Or had been a soldier in a war zone.”
“I work with Help for Heroes and so many people in the forces say, ‘I’m fine, I’m fine’, and they are not fine," she continued. "But I am fine. I was only reporting on it. That’s not to say I wasn’t very badly affected.”
The 63-year-old returned to the town for ITV documentary Return To Lockerbie and saw how people in the town were getting on 35 years after the bombing.
She said she also hopes the documentary will encourage people suffering with PTSD to get help.
Around 73 per cent of people living in Lockerbie at the time of the disaster reportedly suffer from PTSD.
She recalled her own experience: "It was horrendous, eerie, really quiet, with lots of weird smells. But it is the aviation fuel that I remember most.
"The exhausted rescue services searched in vain for people to save. All they could do that night, and in the days to come, was locate and recover the bodies of all of the dead.
"Looking back, as we trudged through that field, I realise I was only able to function and do my job because it felt so utterly unreal. It was like the set of a disaster movie."
Return To Lockerbie With Lorraine Kelly is on ITV1 at 9pm on Wednesday November 15.