The team studied 52 heart attack patients who had been admitted to three major hospitals and were eventually resuscitated. Eleven of the patients reported near-death experiences.

“We found that in those patients who experienced the phenomenon, blood carbon-dioxide levels were significantly higher than in those who did not,” said team member Zalika Klemenc-Ketis, of the University of Maribor in Slovenia.

How carbon dioxide might actually interact with the brain to produce near-death sensations was beyond the scope of the study, so for now “the exact pathophysiological mechanism for this is not known,” Klemenc-Ketis said.

However, people who have inhaled excess carbon dioxide or have been at high altitudes, which can raise the blood’s CO2 concentrations, have been known to have sensations similar to near-death experiences, she said.

Consultants from the addiction centre at St George’s Medical School, London, have published a case report of a British man estimated to have taken around 40,000 pills of MDMA, the active ingredient in ecstasy, over nine years. The heaviest previous lifetime intake on record is 2,000 pills.

(…) he still suffers from severe physical and mental health side-effects, including extreme memory problems, paranoia, hallucinations and depression. He also suffers from painful muscle rigidity around his neck and jaw which often prevents him from opening his mouth.

His condition deteriorated and he began to experience recurrent tunnel vision and other problems including hallucinations, paranoia and muscle rigidity.

For 10 years, MDMA has been suspected of causing these kinds of effects in heavy users. It is thought to be due to its disruption of the regulation of serotonin, a brain chemical believed to play a role in mood and memory.