"I know how crazy it sounds," laughs the Edinburgh-born author. "You would think that the sense of being wrapped up in the body of a 70-foot serpent would be terrifying, but it was far from it.
"I was at a low point in my life and the message seemed to be 'love yourself'. It was a very healing message for me."
The best-selling author of Fingerprints of the Gods, whose latest book Entangled is published today, is describing his first out-of-body experience after ingesting a sacred plant drug known as ayahuasca in the Amazon jungle, where he spent five weeks living with indigenous Indian shamans in Peru.
Since that first trip in 2004, he has returned to the Amazon regularly and has now taken ayahuasca – which he describes as having a "vinegar, battery acid and chocolate" taste – on more than 30 occasions.
The 59-year-old, famed for uncovering lost ancient civilisations, says: "It's the most disgusting and horrific taste that is possible to imagine. Nobody should think you drink ayahuasca for kicks – you have to brace yourself for it.
"The shamans drink it as a religious ceremony which brings them, they believe, into contact with the spirit world.
"Some psychologists might say it's complete nonsense, but frankly these psychologists have never drank it and had the experience to comment on it."
Although Graham describes the experience of drinking ayahuasca as a "two to three-hour extraordinary journey into a parallel world", he does also admit drinking the dark red liquid causes violent sickness and diarrhoea.
The pay-off, Graham explains, for his "intriguing" drug journeys is the inspiration it gives him – the basis for several of his books, including his new novel.
Graham, who has written a book, Supernatural, about shamans, explains: "Shamans have out-of-body experiences and in that altered state they travel, or imagine themselves to travel, into other realms where they have contact with other entities. In order to write the book, I went to the Amazon jungle and drank ayahuasca several times."
It was during one such drug-induced out-of-body experience in the Amazon jungle in Brazil in 2006 that Graham experienced the specific vision which led to his latest book Entangled – his first ever piece of fiction.
"It was almost as though I downloaded the story; suddenly I got the whole notion of two heroines working together to defeat a demonic force.
"It's by drinking ayahuasca that the modern heroine is able to make contact with the Stone Age heroine."
It's not the first time that Graham has gone to extreme lengths to research a book, with his photographer wife Santha, 59 – who also drank ayahuasca with him in the jungle – always by his side.
The couple, who have six children between them and live in Bath, spent six years doing hundreds of scuba dives in various seas around the world in search for underwater ruins.
Graham recalls: "I have been in a situation where the currents were so severe that my mask and regulator were ripped out of my mouth at a depth of 120 feet under water in the Pacific Ocean. I thought that I was going to die, but fortunately one of the support divers helped me.
"The diving expeditions were absolutely worthwhile because we found a huge stone circle larger than Stonehenge off the south west coast of Japan, around 110 feet under water."
Graham's discoveries were reflected in his book Underworld: The Mysterious Origins of Civilisation, which was published in 2002 – the same year his TV series Flooded Kingdoms of the Ice Age was broadcast on Channel 4.
Surprisingly, he was no stranger to near-death experiences from a young age, having had his first one at the age of eight in Edinburgh, where he spent the first three years of his life on Morningside Road before moving to India. He returned to Edinburgh from London to stay with his grandparents in 1958 for a few months, in order to allow his mother to tend to his fatally-ill brother Jimmy.
Graham had never seen snow before, having moved to Vellore in south India in 1954 for four years where his late father Donald, who studied medicine at Edinburgh University, worked as a medical missionary.
Unfortunately, Graham caught pneumonia while walking from Comiston Primary School to his grandparent's house in Morningside during his first ever snowfall. "I was just so excited about the snow that I went out and got completely drenched," he explains. "I was delirious, on death's door. It was very serious."
The ordeal didn't dent his affection for the city, though. Graham, who still regularly visits his uncle James in Fairmilehead, adds: "Edinburgh has always remained the place that I regard as where I come from."
His career has taken him far from the city. After graduating in sociology from Durham University in 1973, he became a journalist, writing for The Times, The Sunday Times, The Independent and The Guardian. In the 1980s, he gave up newspaper reporting to pursue his own passion – the lost civilisation of man. He's written several books over almost three decades, including the best- selling The Sign and the Seal, as well as filming documentaries about his research.
Graham's first number one bestseller was Fingerprints of the Gods – published in 1995.
Hundreds of thousands of pounds in debt, with a second and third mortgage on his house and numerous credit cards maxed out to fund the research, Graham desperately needed the book to be a hit. He says: "
I felt an enormous sense of relief when Fingerprints of the Gods went to number one. If it hadn't been a massive bestseller, I would have gone bust."
The tantalising possibility of a lost civilisation or a forgotten episode in human history has been the focus for many of Graham's books and his research over the last 20 years has taken him to Egypt, Mexico, India and Spain.
Fingerprints of the Gods brought together all the evidence that Graham had gathered of a lost civilisation. It was also one of the inspirations behind Roland Emmerich's latest apocalyptic fantasy blockbuster 2012 – at least according to the film's credits.
Does Graham truly believe that there could be a lost civilisation of man?
He says: "It's not a matter of belief, it is a matter of saying the evidence of our species in the past that we are presented with through the education system is partial, it's not complete.
"Until 5,000 years ago there were no documents at all. We tend to take what we are taught in school for granted and the orthodox view for granted, but the orthodox view was that the sun revolved around the earth and that turned out to be incorrect."
VOYAGE OF DISCOVERY
GRAHAM Hancock's first number one bestseller was Fingerprints of the Gods, which has been a huge worldwide success.
The book, which was published in 1995, has now sold more than three million copies.
It was credited as an inspiration to Roland Emmerich's apocalyptic fantasy blockbuster 2012 by the film's creators.
The book pulls together evidence of a lost civilisation from around the world, with Graham revealing connections he had discovered between the Great Sphinx and pyramids of Egypt, the Andean temples of Tiahuanaco, the Mexican pyramids of the Sun and Moon, and the lost continent that lies beneath Antarctica.
The author's new evidence also suggested the "fingerprints" of an unknown civilisation that flourished during the last Ice Age.