The defining features of a true déjà experience are sudden shock and bafflement, accompanied by the unsettling conviction that what one is experiencing is impossible – and yet it’s happening.

This is different to feelings of vague familiarity with things that remind you of something from your past, or someone you know or have known. Such experiences are not uncommon.

Historically, ‘déjà vu’ has been used as an umbrella term to describe a range of possible déjà experiences.  Physiologists, for instance, have opined that its origin lies in delayed communication between the cerebral hemispheres; psychologists figure these experiences must be due to memory glitch...