Here is an interesting excerpt from the feature by Alasdair McGregor in the Sept 20 Australian Geographic:

Since the syndrome was first clinically documented in the 1940s, psychologists have postulated various triggers and explanations ranging from sensory deprivation, extreme fatigue and boredom, to an evolutionary adaptation. If one person can summon up a benevolent presence while others are incapable of such a thing, then the psychological comfort may give a boost in the survival stakes.

Sy…