Some sleep disorders are well known – sleep-walking for example. But in very unusual cases people who sleepwalk behave in a highly unusual way, this is a very rare form of the disorder somnambulism when they commite violent acts.

In 2008 in the UK a middle aged man with a long history of sleep disorders actually killed his wife whilst they were both asleep. This tragedy happened when they were on holiday and the man in question had decided not to take his medication. He had a nighmare, thought he was struggling with assailants, but when he woke he found his wife dead. There is no reason to suspect that the couple were not happy together, and sleep disorder experts and the police accept that this unhappy case is one of temporary  “insane automatism”.