What physiological response may be responsible for the phenomenon of a near-death experience characterized by out-of-body experiences, the perception of light at the end of a tunnel, and the state of calmness?

Release of Glutamate blockers can cause Near Death Experiences (NDEs).

Glutamate is discharged in plenitude when brain cells die, and on the off chance that it weren't hindered, the glutamate over-burden would make other brain cells to die also. Within the sight of abundance glutamate, the mind discharges its own particular glutamate receptor blocker to protect itself; and it is these blockers scientists speculate as the reason for NDEs.