The Sleep of Reason is a BBC Books original novel written by Martin Day and based on the long-running British science fiction television series Doctor Who. It features the Eighth Doctor, Fitz and Trix.

The Doctor poses as a psychiatrist to investigate strange goings on at a mental health hospital.

• The Eighth Doctor ages about 100 years during this novel, because he travels back in time using a Sholem-Luz portal to shape events at the turn of the century, and then has to sleep in a casket in the cathedral to return to the present.
• The Doctor is always referred to as 'Smith' in this story, except by Fitz and Trix. This is a reference to the classic series, when The Doctor would sometimes call himself John Smith (a very common British name).

• The title is a take from the 1799 Francisco Goya aquatint etching "El sueno de la razon produce monstruos" ("The Sleep of Reason Produces Monsters"), part of the artist's Los Caprichos set.

• The Cloister Library - The Sleep of Reason
• The Sleep of Reason title listing at the Internet Speculative Fiction Database