Sleep researcher Richard Bootzin examines unusual questions related to insomnia, including the link between sleep and resilience in stressful situations.

According to the National Sleep Research project, as many as 16 percent of Americans experience stress-induced insomnia.

Richard Bootzin, a sleep expert and a professor in the University of Arizona's department of psychology, has spent most of his career trying to figure out why, and what people with insomnia can do about it. During that time, he says, he's noticed a sea-change in how people think about sleep.

"Ten or 15 years ago, we never paid much attention to the subject of sleep," he says. "Now we know it affects almost every aspect of our lives, our health, our emotional functioning and how irritable or resilient we are. It affects cognitive functioning and memory. There is almost no area of human functioning that is not impacted by how well we sleep."

Bootzin has become a leading authority on the causes and treatment of insomnia. He developed a therapy using what is called "stimulus-control," which consists of behavior changes that bring his patients back into synch with their natural clocks.

No medications are used; patients are asked to use the bedroom just for sleep, banishing other activities such as eating, reading, watching TV, and even worrying from their beds.

Bootzin is also head of University Medical Center's Insomnia Clinic, where he sees a wide range of patients suffering from difficult sleep problems. One of them is 15-year-old Valerie Portolano, an aspiring writer who was so sleep deprived she was literally walking into walls. Click to watch how Bootzin solved the mystery of Portolano's sleeplessness: