## Facts

- Mr. Sullivan suffered from epilepsy.
- During a postictal state after a seizure, he attacked his neighbor, causing serious injury.
- The incident occurred when Sullivan was confused and acting involuntarily due to his condition.
- The trial judge directed the jury that epilepsy could form the basis for an insanity defence.
- Mr. Sullivan was found not guilty by reason of insanity.
- The prosecution appealed, challenging the trial judge’s directions to the jury.

## Issues

1. Whether epilepsy, as an internal medical condition, amounts to a "disease of the mind" under the legal definition for the insanity defence.
2. Whether the trial judge correctly directed the jury on applying the insanity defence to a case involving epilepsy.
3. How to distinguish between internal and external causes when applying the M'Naghten Rules.

## Decision

- The House of Lords upheld the trial judge’s directions and Sullivan’s acquittal by reason of insanity.
- It was held that epilepsy, despite its physical effects, constitutes a disease of the mind if it results in impairment of mental function.
- The Lords emphasized that the internal origin of the condition was key, considering the epileptic episode as a failure of normal mental processes.
- The decision highlighted that both mental and physical disorders disrupting reasoning could satisfy the insanity defence if they prevent understanding the nature or wrongfulness of the act.

## Legal Principles

- A "disease of the mind" for the insanity defence includes internal medical conditions that impair mental functioning, not limited to purely psychological disorders.
- The M'Naghten Rules focus on the defendant’s reasoning ability and mental control at the time of the act.
- The origin of the condition—internal versus external—is central to determining its classification under insanity.
- The law recognizes that conditions with both physical and mental effects, such as epilepsy, can meet the legal test for insanity if they affect mental faculties.
- Previous decisions, such as Bratty v Attorney-General for Northern Ireland [1963] AC 386 and Kemp [1957] 1 QB 399, were reaffirmed, highlighting the focus on internal causes and their mental effects.

## Conclusion

The House of Lords in Sullivan [1984] AC 156 clarified that internal medical conditions like epilepsy can constitute a disease of the mind under the insanity defence, provided they impair mental functioning and preclude understanding the act or its wrongfulness. This judgment established clear guidelines for applying the M'Naghten Rules to internal conditions, ensuring consistent evaluation of insanity claims.


R v Sullivan [1984] AC 156 (HL)