Eben Alexander's quick trip to heaven started with a headache.
It was November 2008 and a rare bacterial meningitis was fast on its way to shutting down the University of Virginia neurosurgeon's neocortex - the part of the brain that deals with sensory perception and conscious thought.
"For seven days, I lay in a deep coma," he recalled. Yet at the same time, Alexander "journeyed to another, larger dimension of the universe, a dimension I'd never dreamed existed".
There he found "big, puffy, pink-white" clouds against a "deep, black-blue sky" and "flocks of transparent, shimmering beings... quite simply different from anything I have known on this planet".
His travelling partner in the afterlife was a young woman with deep blue eyes and "golden brown tresses" who, amid "millions" of butterflies, spoke to him "without using any words".
Alexander recounts his story, and seeks to explain it, in Proof of Heaven: A Neurosurgeon's Journey into the Afterlife, to be published in the US on October 23.
An excerpt from Proof of Heaven in Newsweek magazine has stirred the enduring debate about life after death.
Inevitably, sceptics wonder if Alexander, who teaches at Harvard Medical School, is going out on a paranormal limb.
"It sounds like he had nothing more than an intense lucid dream," wrote a reader on Newsweek's website. "A personal anecdote is not evidence or proof, as moving as it is," wrote another.
The sarcastic New York blog Gawker challenged its readers to spot the difference between Alexander's portrayal of paradise with published accounts of LSD trips.
But others stood firmly by Alexander, who has previously spoken of his near-death experience on science TV programmes and in a lengthy interview last year with Skeptico.com , a science and spirituality blog.
"If there is evidence and proof of an afterlife, this is probably as good as it gets," Catholic Online, a Web-based Catholic news service, wrote approvingly.
By one estimate, 3 per cent of Americans have undergone a near-death experience. Some have written their stories on the website of the Near Death Experience Research Foundation.
"These experiences might be a glimpse into our next miraculous and exciting adventure," said Paul Perry, co-author of several best-selling books on the topic.
"Unfortunately, there is little meaningful research taking place in this field right now."
Dean Mobbs, a psychologist at Columbia University who studies neurobiology and fear in humans, did not dismiss Alexander's experience - but he questioned how it came about.
"I believe our brains can concoct vivid experiences particularly in situations of confusion and trauma," said Mobbs, co-author of a paper in the journal Trends in Cognitive Sciences.
Mobbs cited research by Swiss neuroscientist Olaf Blanke has artificially induced an out-of-body experience by stimulating the the junction of the right temporal and parietal lobes.
Mobbs said many people who claim to have had a near-death experience were never near death - while most who have died briefly before resuscitation do not recall going anywhere.