Automatism.

The tragic story of the man who strangled his wife in his sleep took me back getting on for thirty years to when I was studying for a law degree. This very situation was discussed in theoretical terms as part of our study of the common law on crime. To be guilty of a crime at common law, it is necessary that you committed an unlawful act (the "actus reus") but also that you did so in an unlawful frame of mind ("mens rea"). Just what amounts to the necessary unlawful frame of mind will vary from crime to crime. But the essence of the situation under discussion is that there could be no mens rea because quite simply there was no mens. You were not under the direction of your conscious mind. Given that there is considerable material on this subject in various text-books, all of which are unanimous that in these circumstances no crime has been committed, the surprise is that a prosecution was brought in the first place.