One man had a vision of his father sailing a canoe towards a huddle of loved-ones on a pier as he took his final breaths.
Neurosurgeon Dr Eben Alexander was convinced out-of-body experiences were hallucinations - until he went into a coma himself and had what he now believes was a glimpse of heaven.
In this second extract from his book The Map Of Heaven, Dr Alexander, who has taught at Harvard Medical School, reveals many others have also seen what he described.
A near-death experience will change your life in more ways than one. It means you have survived a serious illness or a major accident, for one thing, and that alone is one of the most significant events imaginable.
But the aftermath, as you adjust to your radical new perspective, can be even more significant. For me, it was as if my old world was dead and I had been reborn into a new one.
Coping with that is hard: how do you replace your old vision of the universe with a new one, without unravelling into chaos?
How do you take that step from one world to another one, without slipping and falling between the two?
So many people are going through similar versions of what I went through, and the stories I have heard from other near-death experience witnesses give me courage every day. They are a constant corroboration of everything that was revealed to me - how we are loved and cherished much more than we can imagine, how we have nothing to fear and nothing to reproach ourselves for.
If you have never seen yourself as a spiritual person, and perhaps did not even believe in God, this new dimension to your understanding has an even greater impact.
A man named Pascale wrote to tell me about his father, who had a PhD in astrophysics and was '100 per cent scientifically minded' - in other words, a complete atheist.
Pascale's dad (we'll call him Pierre) was a heavy drinker. He'd suffered a succession of emotional blows, and he used hard drink to numb the pain - so much that his organs started one by one to pack up. Kidneys, liver and then lungs gave way, and Pierre succumbed to double pneumonia.
He was not expected to live, but to give his body the best chance of repairing itself, the doctors placed him in an induced coma.
After three months in intensive care, he started to come round - and all this hard-headed scientific man wanted to talk about with his son were his experiences of heaven.
He had seen the after-life, just as I did. And he brought back the same message: there were angel-like beings who loved us more than we could imagine, and they would help us, if only we would let them.
Pierre faced a major challenge. He could never drink again. One glass would be enough to tip him back into alcohol abuse, and the end would be inevitable.
The stories I have heard from other near-death experience witnesses give me courage every day
Somehow, he found the strength to beat his demons. For the next four years, Pierre didn't touch a drop. But after his initial burst of spiritual fervour in the hospital, he stopped talking about heaven.
Pascale sensed that his dad, an intensely shy man, was embarrassed by the massive contradiction between the atheism he had always preached, and the heaven he had experienced during his coma. He found it easier to say nothing.
But he developed a quirky habit, which seemed to help him in his abstinence - in all the places where he might be tempted to relapse and have a drink, Pierre left Post-It notes. Every one was the same, with four cryptic letters written on it: GaHf.
Pierre would not say what the notes meant. All he would admit was that they helped him.
After four years, his heart gave out, and Pierre died. His son was deeply comforted by words his father had said in the hospital: 'I'm not afraid of dying any more. I know it'll be fine.'
Not every experience of heaven and the change is brings is so dramatic as others. One woman recalls feeling an overwhelming sensation of love at the exact moment her mother died.
After the funeral, as he collected up the Post-It notes, Pascale had a sudden insight. He knew what the letters GaHf meant, what his father was reminding himself . . . 'Guardian angels. Have faith.'
Not every experience of heaven, and the change it brings, is so dramatic. After I first shared my story with others in public, I received a charming letter from a lady named Jane-Ann, who told me that she underwent surgery for a brain abcess in 1952, when she was eight years old, and that for two weeks after the operation she was in a coma.
Her mother was beside her bed when she awoke, and what Jane-Ann remembers clearly is the expression of deep concern on that beloved face. Simply and matter-of-factly, as only a child can, Jane-Ann explained that there had never been any reason to worry - she had been with her great-aunt Julie, sitting on her lap and being comforted.
Sixty years later, that image of her great-aunt was one of her clearest memories.
Sometimes, it is the death of a loved one that induces or inspires a near-death experience in us. A lady called Jean wrote to tell me what she had experienced when her mother died, in 1980.
On a Saturday afternoon, Jean was in her garden. She was due to fly to New York on the Monday, to visit her mother who was being treated for cancer in hospital, and who was not expected to live more than six months.
As she tended her flowers, Jean was suddenly overwhelmed by 'a feeling of an unbelievable amount of love'. It passed through her, like a puff of air, and left her feeling exalted. As she stood wondering what she had just felt, the sensation travelled through her again, pervading every cell in her body.
No sooner had the feeling faded than it happened a third time. And suddenly, Jean understood what it meant. Her mother had died, and was telling her how much she loved her, as she departed this realm and embarked on her voyage through the next.
The feeling that Jean had initially thought was simply going through her had in fact enveloped and encompassed her, as only love can.
Sometimes, it is the death of a loved one that induces or inspires a near-death experience in us
'The feeling was like she was hugging me but going right through me. And every time she did this, I felt this supernatural, unbelievable, immeasurable amount of love.'
Jean went to sit by her phone in the house. She knew what would happen next, and within ten minutes it did: her sister phoned from New York, to tell her their mother had passed away.
As she wrote that letter, Jean told me she was crying - tears of joy, not of sadness. Ever since that moment in the garden, she has felt utterly safe and loved, confident that she will be reunited with her loved ones in heaven, and safe in the knowledge that death is nothing to be feared.
In fact, she confesses, she sometimes feels almost envious when people pass away.
One of the most extraordinary things about my own glimpse of heaven was that, back in this world, no one was aware of the transformation that I was undergoing. All the monitors and sensors and computers could detect no activity: my brain was flat-lining.
But sometimes, the eyes of those we love can see the change, as a sort of spiritual radiation.
A man called David experienced exactly that, when his father died. With his three siblings, he was sitting in a private room at a hospice where his dad had been for 13 days. They had kept a constant bedside vigil, and it was plain that the end was near.
At 4am, with the room in darkness except for a single night-light in the wall, their father took his last breath - and as he did, a speck of glowing dust seemed to settle on his temple. It was like a pinprick of gold.
No light was shining on the old man's face, yet this particle of dust was vivid and luminous. As David watched, it began to swell into a pea-sized orb. Now it was a translucent blue, like the light underneath a candle flame. White rays sparkled from it.
The orb lifted, hovered, and then drifted across the room, still effervescing with sparks, until it disappeared through the ceiling. David followed it with his eyes, not daring to speak, until it was gone - and then he turned to one of his sisters. 'Did you see that?' he asked.
His sister said: 'You mean that light that just came out of the side of Dad's head?'
People ask themselves these questions all the time, when a loved one passes and something inexplicable, something beyond the purely physical, occurs. We know what we've seen, but we can't quite bring ourselves to believe it, without corroboration from someone else: 'Did you see that?'
Perhaps the most extraordinary story of a near-death experience was told to me by John, the son of a war veteran, who believes he accompanied his father on the first stage of his journey into heaven.
His dad was a fighter, an ex-prisoner of war who was clinging to life in his hospice bed despite having suffered a massive pulmonary embolism.
His breathing was very laboured, and John was kneeling at the bedside, holding his hand, with his ear close to his father's chest - when suddenly, he was thrown into another dimension.
Dr Eben Alexander was convinced out-of-body experiences were hallucinations until he went into a coma himself.
he said: it was like being immersed in a 3D movie. His perspective was airborne, like a helicopter shot, and he was looking down at a rapid stream, flowing over rocks.
In the water, clinging on for dear life, was his dad. A golden glow began to spread across the water, like a celestial spotlight. In the middle of the light, a white canoe appeared, with a red paddle, floating quite still on the rushing water.
With a shout of excitement, his father let go of the rocks and began to swim for the canoe. Suddenly, he wasn't a sick old man any more - he was an athlete, with the strength of a man in his 20s.
He leapt into the canoe, and John felt himself race down, like a camera zooming in, to ride behind his dad's shoulder.
His father turned and gave him a look of such love and joy as he had never seen on his face before. And then the perspective changed again, and John was high in the sky, watching as the white canoe raced towards a jetty where dozens of people were waiting and cheering.
He recognised them all - family members, friends and war buddies of his father's.
As the canoe docked, he saw his dad stand up and raise the paddle in a salute, grinning and almost beside himself with delight. Then he leapt ashore and disappeared into a huddle of embraces and back-slaps.
At that moment, John found himself back at the bedside. His father's heart had stopped.
'This experience was transformative, a gift from my dad I could not repay,' he wrote to me. 'I can actually feel myself glowing when I tell this story!'
New knowledge like this changes us for ever. It must do - that is its purpose. We evolve into someone fresh.
That's what happened to me after my near-death experience, and to every one of the people in these stories.
