This is interesting regarding the nature of consciousness and near-death experience:
The brain is both sophisticated and delicate. For instance, if oxygen is reduced by even a small amount, the brain will react almost immediately. As a result, many scientists suggest that near-death experiences are the result of physical changes in the brain, like the lack of oxygen, that takes place when the brain is stressed or dying.
During the study, which was referred to as AWARE (awareness during resuscitation), the researchers studied a broad range of awareness and mental experiences associated with cardiac arrest. Of the 2,060 patients enrolled in the study, 330 survived and 140 we able to complete structured interviews about their memories of the event.
What the researchers discovered is that nearly 40 percent of these individuals described some awareness of the time prior to resuscitation, or when their hearts stopped beating. The majority of these patients did not have any specific memories of the event though. What this suggests is that many people do have mental activity during cardiac arrest, but often lose their memories of that activity after recovery. According to the doctors conducting the study, this could be due to brain injury or sedative-like drugs.