The research, which appeared in the scientific journal Neurology, has attracted international attention. The report's lead author says it should be possible to test the theory.
The UK researchers argue that near-death experiences may be caused by a blurring of waking and sleeping states brought on by a biological mechanism.
Individuals who have reported near-death experiences appear to be more likely to have a strong "fight or flight" arousal system. In moments of extreme stress, that system can cause them to experience some features of deep sleep despite being awake, the study said. The state of deep sleep, know as REM, or rapid eye movement sleep, is the part of sleep during which most dreaming occurs.
The jarring experience triggers the REM sleep state to briefly kick in even though they remain awake, said Dr. Kevin Nelson, a UK neurologist who led the study.
The UK group interviewed 55 people who reported near-death experiences after car wrecks, heart attacks and other nearly fatal events.
Researchers found that 60 percent of them had had at least one previous occurrence of REM sleep while they were awake. In comparison, only 24 percent of people in a separate group of 55 individuals who never had a near-death experience reported having had "REM intrusion" while awake.
Nelson said near-death experiences are not necessarily considered dreams, noting that the two sensations are fundamentally different. Further, he said, the UK report should not threaten anyone who believes that near-death experiences are proof of an afterlife. The study only suggests a biological explanation of how the experiences happen, Nelson said.
People who report near-death experiences appear to have an arousal system that predisposes them to REM intrusion on wakefulness, which could set the stage for near-death experiences, the UK researchers said.
"We're not saying that REM intrusion explains everything," Nelson said. "We know there's a confluence of factors. But this actually is the first testable hypothesis for the basis of near-death experiences, and that's really where it's important."
Nelson declined to describe how such a test might be done, calling that a "subject for additional inquiry."
The UK report has drawn high marks from experts.
"It's a great study," says Dr. Mark Mahowald, director of the Minnesota Regional Sleep Disorders Center. "The bottom line is that, unlike what most people think, sleep is not all or nothing. You can have bits and pieces of sleep intruding into bits and pieces of wakefulness, and that's where things get interesting."
The term "near-death experience" was coined by Dr. Raymond Moody, a doctor and philosopher, in his 1975 book, "Life After Life."
Moody, who said he has seen the UK report, says he welcomes any study that sheds new light on near-death experiences. But he said he doubts that any scientific explanation will sway those who passionately believe that these experiences prove life doesn't end at death.