The sleeping brain, left to its own devices, rules an eccentric, sensual and sometimes violent landscape.
When she woke up to find her husband on top of her in the middle of the night, Vanessa Otts tried waking him, but she says he didn't wake up.
"My clothes were pretty much off and his clothes were off, and all of a sudden, he just rolls back over and goes back to sleep," Vanessa says.
When Vanessa told Tyson that he tried having sex with her during the night, he denied doing anything to her. "I think I would remember almost having sex with you," he says. " There's no way that that happened."
The Otts have a strange but real problem. In the five years of their marriage, Tyson routinely initiates sex with his wife when he is sound asleep.
Doctors have given this act of sex while sleeping a medical-sounding name: sexsomnia.
Nancy Foldvary, the director of the Sleep Disorders Center at the Cleveland Clinic, calls the problem "real."
Foldvary says she's primarily seen men with this disorder, men who have come to her because their bed partners were complaining. "He just gets really aggressive, I guess you could say. He's actually become more physical, like holding me down, or taking my shirt off, or, you know, forcefully kissing me," Vanessa says.
Tyson says the scary part is that he has no recollection of his actions during the night.
So is it possible for someone to rape an individual and claim he was sleeping when he did it?
Foldvary says it's possible that a person "could have sex without any memory for it, during a sleep state."
In cases around the world people have used sexsomnia -- sometimes successfully -- as a legal defense for rape.
Mike Mangan is a research psychologist at the University of New Hampshire and acknowledges people use this defense.
"People walk in their sleep. They talk in their sleep. People do all kinds of crazy things in their sleep," he says. "And it just hasn't entered the popular mind that sexual behavior is just another type of behavior that occurs in sleep."
As for the underlying causes of sexsomnia, researchers have begun focusing on what amounts to a "mind-body disconnect," a disconnect between our primal urge for sex and the cortex of the brain that controls rationality and judgment.
"Basically, what you have is a sexually motivated body and a cortex that has switched off. When that's switched off, you have a sexually active body that is having its way," says Mangan.
Though sexsomnia is clearly unusual, researchers say the actual number of cases is underreported, and it shows up in both men and women. The cases, however, are rarely caught on tape.
Lori Norman told what happened to her one night while sleeping with her husband, Bob. "I woke up with him pounding the pillow right beside my face. I mean within inches of my face."
Lori and Bob have become accidental combatants in a nocturnal prizefight. Repeatedly during their nine-year marriage, a sleep disorder has caused Bob to unwittingly assault his wife.
"We were sound asleep, and he takes his two hands with his fist together and pounds the back of my neck. And I just screamed, and I threw my hands up over my head, and I grabbed his hands, as they were coming down again," Lori says.
Keep in mind that in every other way, the Normans say they're a loving, happy couple. When her husband is not sleeping, Lori says, "He just exudes this peacefulness."