Near-Death Experience
The near-death experience (NDE) is the set of phenomenological experiences reported by people who came close to clinical death and survived: feeling of leaving the body, tunnel of light, encounter with deceased loved ones, "life review", overwhelming peace. Scientific study popularized by Raymond Moody (Life After Life, 1975).
Scientific explanations
Neuroscience explains many elements: cerebral hypoxia (tunnel), endorphin release (peace), reactivation of episodic memory (review), DMT in the dying brain. But the qualitative experience remains intriguing.