A phenomenon that appears to be closely related to the NDE is the Shared Death Experience (SDE) as coined by Raymond Moody. In these experiences, bystanders who are close to a dying person experience many of the same aspects of the NDE along with the dying person, including leaving their bodies, meeting beings of light, and seeing the life review of the dying person. These bystanders are themselves healthy and not dying yet seem to share these experiences. This seems to disprove the common theory that NDE-type experiences are caused by the dying brain. Raymond Moody’s book ”Glimpses of Eternity” discusses his research on this topic.
Here are some reasonable external references I have been able to find: