The Awareness during Resuscitation (Aware) study, sponsored by the University of Southampton in the UK, used objective markers to establish whether the experiences were real or hallucinatory.

The results showed that 39 per cent of patients who survived cardiac arrest described a perception of awareness but did not have explicit recall.

A total of 46 per cent experienced a broad range of mental recollections, nine per cent had experiences compatible with NDEs and two per cent exhibited full awareness compatible with OBEs with explicit recall of "seeing" and "hearing" events.

And one case was validated and timed using auditory stimuli during cardiac arrest.

"This is significant, since it has often been assumed that experiences in relation to death are likely hallucinations or illusions, occurring either before the heart stops or after the heart has been successfully restarted, but not an experience corresponding with 'real' events when the heart isn't beating," Dr Parnia said.