What is the difference between the defences of insanity and automatism

Insanity is the 'defect of reason, due to a disease of the mind as to not know the nature of his act or if he did, he did not know it was wrong' as set out in M'Naughten . In order to understand the requirement of insanity, it is necessary to break down the test created in M'Naughten and look into the cases which explained it. Defect of reason requires the defendant (D) to be impaired, however, as set out in Clarke , it is not enough to be absentminded and confused for it to constitute as a defect of reason. Following this, it is necessary to establish what disease of the mind is. It was argued in Sullivan that an illness which had a physical impact on the body such as epilepsy was still a disease of the mind as it affected the mind nevertheless. In Kemp, it was held that the hardening of the arteries was an external illness which affected the mind. Difficulty comes with diabetic cases where it is necessary to establish when the insulin was taken or not before deciding if it is insanity. In Hennessy, the defendant did not take their insulin which resulted in them having a hyperglycemia episode, it was held to be insanity as it was a disease of the mind caused by the diabetes as a result of the insulin not being taken. However, in Quick, the defendant took the insulin but did not eat resulting in them assaulting a patient, this was an external effect which as we will see later, is automatism.
Bratty describes automatism to be the 'act done by the muscle without any control by the mind where the defendant is not conscious of their actions'. The definition does not allow driving without awareness as it is not 'total destruction'(AG Ref 1992) Similarly, in diabetic cases as seen in Quick, the external factor which is insulin means that there is automatism as it is not a disease of the mind causing the action, rather it is the insulin affecting the body. In Bailey, it was held that self induced automatism only applies to offences which carry intent as the mens rea to show that otherwise not under automatism, they would not commit the offence.