Near-death experiences, or NDEs, are experiences during which are person feels he died (in some cases having actually been declared clinically dead), and came back to life. People who experience NDEs often claim that they saw a tunnel, dead relatives, and talked to religious entities, such as god or angels, who after some time told them to go back to life. Some theists use this as direct evidence of the existence of god.
However, this perception is explained by psychology. In 2011, the Edinburgh University and the Medical Research Council in Cambridge reviewed existing research, concluding that "The scientific evidence suggests that all aspects of the near-death experience have a biological basis" (http://www.bbc.co.uk/news/health-15494379).
Also, a person's vision of an afterlife during a NDE is as described by their religion. Christians talk to god, Muslims to allah, etc. Since these beliefs are mutually exclusive, NDEs couldn't be used as evidence to support a specific religion even the evidence against it being a religious experience was disconsidered.