There may be a small amount of life after death, scientists believe.
The largest ever medical study into near-death and out-of-body experiences has discovered that awareness may continue even after the brain has shut down completely.
It is a controversial theory which has, until recently, been treated with widespread scepticism.
Scientists at the University of Southampton spent four years examining more than 2000 people who suffered cardiac arrests at 15 hospitals in the UK, US and Austria.
They found that nearly 40 per cent of those who survived described some kind of "awareness" during the time when they were clinically dead before their hearts were restarted.
One man even recalled leaving his body entirely and watching his resuscitation from the corner of the room.
Despite being unconscious and "dead" for three minutes the 57-year-old social worker from Southampton, recounted the actions of the nursing staff in detail and described the sound of the machines.
"We know the brain can't function when the heart has stopped beating," said Dr Sam Parnia, a former Southampton University research fellow now based at the State University of New York, who led the study.
"But in this case conscious awareness appears to have continued for up to three minutes into the period when the heart wasn't beating, even though the brain typically shuts down within 20-30 seconds after the heart has stopped.
"The man described everything that had happened in the room, but importantly, he heard two bleeps from a machine that makes a noise at three-minute intervals.
"So we could time how long the experienced lasted for.
"He seemed very credible and everything that he said had happened to him had actually happened."
Of 2060 cardiac arrest patients studied, 330 survived and 140 said they had experienced some kind of awareness while being resuscitated.
Although many could not recall specific details, some themes emerged.
One in five said they had felt an unusual sense of peacefulness while nearly one third said time had slowed down or speeded up.
Some recalled seeing a bright light; a golden flash or the sun shining.
Others recounted feelings of fear or drowning or being dragged through deep water. In addition 13 per cent had felt separated from their bodies and the same number said their senses had been heightened.
Dr Parnia believes many more people may have experiences when they are close to death but drugs or sedatives used in the process of resuscitation may stop them remembering.
"Estimates have suggested that millions of people have had vivid experiences in relation to death but the scientific evidence has been ambiguous at best.
"Many people have assumed that these were hallucinations or illusions but they do seem to correspond to actual events.
"And a higher proportion of people may have vivid death experiences, but do not recall them due to the effects of brain injury or sedative drugs on memory circuits.
"These experiences warrant further investigation."
Dr David Wilde, a research psychologist at Nottingham Trent University, is compiling data about out-of-body experiences in an attempt to discover a pattern which links each episode. He hopes the latest research will encourage new studies into the controversial topic.
"Most studies look retrospectively, 10 or 20 years ago, but the researchers went out looking for examples and used a really large sample size, so this gives the work a lot of validity.
"There is some very good evidence here that these experiences are actually happening after people have medically died," Dr Wilde said.
"We just don't know what is going on. We are still very much in the dark about what happens when you die and hopefully this study will help shine a scientific lens onto that."
The study was published in the journal Resuscitation.
Dr Jerry Nolan, editor-in-chief at Resuscitation, said: "Dr Parnia and his colleagues are to be congratulated on the completion of a fascinating study that will open the door to more extensive research into what happens when we die."