"I had all my life before me," he said. "I started dreaming how I would be executed every time I closed my eyes."
Aygun, an award-winning reporter for Turkey's Milliyet daily, was kidnapped by Islamic State (IS) jihadists in November 2013 and held for 40 days.
He has now published a book on his experience, "40 Days at the Hands of IS", which lays bare his emotions and reflects the complexity of Aygun's own relations with his captors.
"If I hadn't written it, I would have betrayed my colleagues," he told Agence France-Presse in an interview.
Aygun, who spent his entire period in captivity blindfolded and his legs tied together with ropes, said on many occasions he feared he would never come back.
"Those 40 days felt like 40 years. I was a prisoner of ISIS," he told AFP at Milliyet's headquarters in Istanbul, using an alternative name for the group.
- 'This is the end' -
Aygun was seized by IS militants -- together with a commander of the Western-backed rebel Free Syrian Army (FSA) -- while on his way to interview a group of jihadists in the town of Salkin on November 25, 2013.
The announcement he was going to be executed was made by a man he called "Dayi" (uncle) whom he befriended during his captivity. Dayi would bring him food and drinks everyday and used to tell him things that gave him hope.
"I would love to save you, but unfortunately I couldn't. The qadi (an Islamic judge) ruled for your execution."
Aygun waited for three days, planning to attack the guards when they entered his cell so that they would kill him with a bullet instead of a sword. But no-one came.
"The silence, loneliness and uncertainty was enough to make me go insane but a divine power helped me keep my sanity."
"Awaiting my death was the worst form of torture."
On the third day the guards came, saying that Dayi had died in fighting and they would execute him themselves.
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They showed him the man's body and made him kiss and smell it, saying he would smell like that when he was "martyred."
Then one day armed men stormed the building where he was being held.
"I said: 'This is the end. They are going to take me outside and behead me.'"
But none of the IS fighters turned up to take him away when the time came. He was alone for three days, wondering if they had left him to starve.
Aygun was eventually freed by a rival group one night and returned home to Turkey.
- 'Such a relief' -
Unbeknown to Aygun, IS had withdrawn from the town where he was being held and a rival group had taken control. Turkey's National Intelligence Organisation (MIT) had also been holding talks for his release.
This was before IS conducted its most notorious killings of the foreign journalists and aid workers it was holding, starting with the US reporter James Foley.
Aygun admitted being a Turk was a real "advantage", saying a Muslim fellow hostage showed him how to pray and he was treated with more respect after he taught others the same.
The prayers, five times a day, were the only time his blindfold was removed.
"It was painful to write the book, going through the same feelings, but I felt such a relief afterwards."
He said he had been beaten up and tortured and in the most extreme case was forced to eat in the presence of hostages who were about to be hanged.
But the details of the brutality he experienced and how he feels about them were not included in the book.
"The things I've experienced left me deeply scarred in many ways but they are not so important when you consider how many people are brutally killed (by IS) every day," he said.
After a period of recuperation, Aygun is now back at his job at Milliyet.
"Everyone knows how they (IS) treat people. I wanted to tell something people didn't know."