Henry VI: What Was The King's Great Mysterious Illness?

It was August1453. King Henry VI of England left his pregnant wife Margaret of Anjou at home and travelled from court to the West Country on a judicial visit. Stopping off at Clarendon Palace in Wiltshire the 31-year-old king was, “suddenly…taken and smitten with a frenzy and his wit and reason withdrawn”. What was the terrible and mysterious illness that struck down Henry VI who was a central figure in the Wars of the Roses?