The temporary (symptoms resolve in 24 hours or less) loss of one’s short-term memory.

Example: A fifty-five-year-old smoker is suddenly unable to recall any events from the past few hours. His condition clears after approximately half a day.

I think the best resource on this concept is here at the MayoClinic link: http://www.mayoclinic.com/health/transient-global-amnesia/DS01022