What type of disease was identified as a "disease of the mind" in R v. Sullivan?

In the case of R v. Sullivan, epilepsy was specifically identified as a "disease of the mind" for the purposes of criminal law. The ruling established that a person suffering from a condition that affects their mental faculties, such as epilepsy, could be deemed to lack the necessary mens rea, or guilty mind, required to commit certain offenses. This definition is significant in determining the legal culpability of individuals suffering from such conditions during the time of the offense.

The court's reasoning revolved around the idea that the effects of the condition – in this case, seizure episodes resulting in impaired consciousness or judgment – align with the understanding of mental disorders that can substantially impact a person's ability to act in accordance with the law. This case set a precedent regarding how mental health conditions are evaluated within the context of criminal responsibility.