Because automatism is such a comprehensive defence, there are various exclusions to an automatism defence. The person must not be at fault. The classic example of this is falling asleep at the wheel of a car (
Kay v Butterworth). Although one is not responsible for acts done while asleep, one can be held responsible for driving in a state where one would fall asleep at the wheel. The issue of prior fault applies to many diabetics who suffer hypoglycaemia while driving. Voluntary (and often involuntary) intoxication cannot cause legal automatism. In many jurisdictions, there is a distinction made between "sane automatism" and "insane automatism". Where the involuntariness is caused by a mental illness, or "disease of the mind", as per the
M'Naghten rules, it will be regarded as "insane automatism" and will often result in a special verdict of "not guilty by reason of insanity". This can have significant practical effects for the defendant, as they still may be detained after a special verdict as opposed to the straight acquittal available through sane automatism. The M'Naghten rules require a "disease of mind", which requires an internal cause. This is medically nonsensical, and does not always bear much relationship to continuing risk which is the main justification. This means that insane automatisms do not require total loss of voluntary control (see below). Thus they are easier to prove in some circumstances, but conversely the burden of proof is on the defendant. Sleepwalking was initially an exception to the internal-external doctrine until the case of
R v Burgess. The most contentious qualifier is that there must be a total loss of control. In ''Attorney-General's Reference No 2 of 1992
, this definition of legal automatism was confirmed. A lorry driver had crashed, and his defence (backed up by expert evidence) was that the monotony of motorway driving had caused him to go into a state of "driving without awareness" where, although he could make minor adjustments to follow the road, he was not truly conscious of driving. This followed the decisions of Watmore v Jenkins
and Broome v Perkins'' where diabetic drivers who had driven three miles or more were held to not have the total loss of control necessary for the defence of automatism. This definition is problematic, and the Law Commission, Butler Committee and leading legal academic R. D. Mackay have all argued that this definition is too restrictive. Classically automatisms in the legal sense have been defined as spasms, reflexes, convulsions or acts committed in a state of unconsciousness e.g. sleep. However, there have been cases where the automatism defence was successful when none of these apply. In
R v T the defendant had been raped a few days prior to committing a robbery. She was clearly conscious of what she was doing, but in a dissociative state due to post-traumatic stress disorder from being raped. However, in
R v Isitt, when the defendant drove away from a collision and evaded a police roadblock in a dissociative state, the defence was not successful. The Ontario Court of Appeal expressed a logical way of distinguishing such cases in
Rabey v The Queen. There, the defendant went into a dissociative state due to being spurned. It was held that such a commonplace occurrence was not the sort of external stimulus that would cause legal automatism (although the insanity plea would be open to him). ==Omissions==