A 'core' near-death experience reflects — as intensity increases according to the Rasch scale — peace, joy and harmony, followed by insight and mystical or religious experiences (Lange, Greyson & Houran, 2004). The most intense NDEs involve an awareness of things occurring in a different place or time. Among the clinical circumstances that are thought to lead to an NDE we find such factors as: cardiac arrest, shock in postpartum loss of blood or in perioperative complications, septic or anaphylactic shock, electrocution, coma, intracerebral haemorrhage or cerebral infarction, attempted suicide, near-drowning or asphyxia, apnoea, serious depression (van Lommel et al., 2001).
Worth a read.
Here's a compelling YouTube entry about the subject: