Graeme Scott, 44, from Irchester, Northamptonshire, was on holiday with his parents and cousin when the killing spree took place on June 26 last year.
He told the Press Association that the family have struggled to sleep and he has been reluctant to visit some busy places because of what happened.
“We were waking up in the middle of the night hearing gun shots and panicking,” he explained.
“It took me a long time to go to the local shopping centre because you didn’t know who was in front or behind you or where the escape route was.”
“It’s there every day. You’re always thinking about the situation.”
Mr Scott and his family were lying by a swimming the pool when they first heard gunshots as Seifeddine Rezgui went on the rampage.
He and his parents Jen and Sid ran into the Hotel Imperial Marhaba and hid in a cellar with around 20 people, while his cousin Karl took refuge elsewhere.
Once the attack was over they emerged from their hiding place to see a number of dead bodies and blood.
“It was a sight that will live with us for a long time,” he said. “It’s very hard still to this day.”
Mr Scott, a warranty manager at a vehicle retailer, explained that when he hears about other terror attacks such as in Orlando, Paris and Brussels, it “brings it all back”.
Seifeddine Rezgui was shot dead by police after carrying out the attack, which terror group Islamic State claimed responsibility for.
“It’s a strange feeling ... he will never be able to apologise for what he’s done,” Mr Scott said. “To a degree it’s sad that nobody has been accountable.
“It’s something that I will have to live with for the rest of my life, but being a Christian the forgiveness will be there.”
A number of survivors from Sousse have stayed in touch with each other through social media.
This has been a comfort and created friendships, Mr Scott said.
Asked whether he would consider returning to Sousse, he replied that it is “still very raw” but he occasionally thinks he would like to go back to see the hotel staff.
He will spend the anniversary with around 40 other British survivors who will meet for a private service and lunch.