The Discworld novelist, who suffers from Alzheimer's disease, was midway through a three-city book signing tour of the U.S. to promote his new novel Dodger when the terrifying incident occurred.
His assistant, Rob Wilkins, had to perform emergency cardiopulmonary resuscitation (CPR) in the cab and he insists the author could have died without his help.
Wilkins tells NewStatesman.com, ""I had to kneel on the back seat of the taxi and give him CPR. It was fingers down throat stuff. He nearly died.""
Pratchett was taken to hospital where doctors told him he had suffered an atrial fibrillation, a condition which causes an irregular and abnormally fast heart rate, brought on by the cumulative effect of prescribed blood pressure drugs and the pressures of his busy touring schedule.
However, the author recovered quickly and even joked about the incident: ""I once heard it mentioned that signing tours can kill you quicker than drugs, booze and fast women.""