This reminds me of a documentary I saw once about sleepwalking. Some sleepwalkers can get violent but not realize it. One guy killed a girl in his sleep and used it as his murder defense, but he was found guilty.
Many cases, different verdicts.
Homicidal sleepwalking - Wikipedia, the free encyclopedia
In regards to your question, like someone else said, polygraphs aren't admissible in court, so how one scores on a polygraph shouldn't matter.