During the day, Lawrence Neumann was a mild-mannered man, considerate, kind and loving to his wife of many years, Bonnie.

In the middle of the night, as they tried to sleep, he became someone else, screaming obscenities, grunting, kicking, punching Bonnie in the arm, violently hurling himself out of bed.

For sixteen years, this couple from Streator, Ill., had no idea what was happening or why, night after night. Their local doctors were at a loss to explain the strange symptoms. "Nobody seemed to know anything about it," said Lawrence, 73, now retired from a concrete block business.

Relief came at long last nearly two years ago in the form of a diagnosis from a neurologist at Northwestern University's Feinberg School of Medicine. Lawrence had a little-known condition, REM sleep behavior disorder, in which people act out their dreams, unconsciously, during sleep. That diagnosis was a turning point, because the condition is easily treatable.

Nine out of 10 people who suffer the disorder are men. The vast majority are 50 or older, although new research is finding a higher prevalence of the disorder in younger adults as sleep problems gain more attention, according to Dr. Bradley Boeve, a professor of neurology at the Mayo Clinic and a leading expert on this condition.

"Several patients we've seen, their spouse will describe first encountering this on their wedding night," he said.

Estimates suggest 1 in every 200 adults has the strange affliction, caused by a dysfunction in a part of the brain that suppresses muscle activity while people are in REM sleep, a dream-filled phase of slumber.

The prevalence of REM sleep behavior disorder might be much higher in seniors. Notably, 9 percent of 2,300 adults age 70 to 90 surveyed in Olmsted County, Minn., reported symptoms consistent with the diagnosis. "Even if only half actually have it, that's still 4 to 5 percent — and that makes it pretty common," Boeve said.

A growing body of research suggests the condition is a precursor to Parkinson's disease and Lewy body dementia in up to 25 to 50 percent of patients. Why that is so is not yet clear, but neurons in adjacent areas of the lower brain stem appear to be implicated, according to Dr. Carlos Schenck, one of the physicians who first described REM sleep behavior disorder.

Scientists are monitoring patients closely and hoping that drugs will become available to prevent neurodegenerative disorders from developing after the first signs of REM sleep behavior disorder appear.

Asked about patients, Schenck described men who have jumped through windows while asleep, choked their bed partners, smashed into dressers, knocked themselves unconscious and given their wives black eyes. Their experiences are eerily similar: men dream they're being chased or hounded by large insects, animals or threatening people and have to defend themselves, Schenck said. Almost inevitably, the dreams are colored by violence and aggression.

One of Schenck's patients is Cal Pope, 85, of Circle Pines, Minn., who had seen 400 men go down on a ship in the South Pacific in World War II. "I was sure he was reliving that," said his wife, Rowena, 81, who would watch Cal kick the wall fiercely and threaten to crush people's heads in the middle of the night. It took nine years for Pope to get a proper diagnosis and treatment.

One night, Rowena watched in horror as her husband got down on all fours, roaring like a lion. "I was chasing other lions around," Cal remembered, adding that he was frequently "completely worn out in the morning" after nightly episodes.

To be evaluated, patients need an expert sleep study, with electrodes placed on their arms and legs to track movements during slumber, said Dr. Alon Avidan, an associate professor of neurology at Ronald Reagan UCLA Medical Center. A video will capture the patient's activities and other conditions, such as sleep apnea, that can cause similar symptoms. Also, alcohol, coffee and certain antidepressants can serve as triggers for REM sleep behavior episodes.

Symptoms are relieved 90 percent of the time by clonazepam (also known as Klonopin), a medication commonly used to treat anxiety, panic attacks and seizure disorders. It helps patients sleep more soundly, wake less often and have fewer episodes. A large number of patients also are helped by melatonin, which is being studied at Northwestern as a treatment for REM sleep behavior disorder.

In California's San Diego County, John Chadwick used to strap himself into bed with a seat belt and put on leather handcuffs so he wouldn't hurt his wife, Susan, in the middle of the night. Once, Susan said, "he kicked me out of bed so hard I landed on my head." Another time, she remembered, "he bit me so hard on my wrist that the teeth impressions lasted for two days."

"I was living a nightmare," said John, who is being treated successfully with melatonin at UCLA.

For Lawrence and Bonnie Neumann, night became a time of danger. Once, after leaping out of bed in the midst of an episode, Neumann hit his head on a nightstand, opening a large gash. Another time he threw himself out of bed head first, smashing his forehead on the floorboards and causing a concussion.

It was routine for Neumann to start kicking his wife, dreaming a bear was sneaking up on him. "The mood was one of defense against attack," he remembered. "If she tried to touch me, I'd come after her."

Bonnie Neumann put pads around the bedroom furniture so Lawrence couldn't hurt himself; other couples take sharp objects away, put mattresses on the floor, arrange foam barriers between them or move their bedrooms to the ground floor so they don't leap out of second-story windows.

"It's very important to take safety precautions, kind of like baby-proofing the room," said Dr. Phyllis Zee, associate director of Northwestern University's Center for Sleep & Circadian Biology.

After extensive neuropsychiatric tests and three separate sleep studies, Neumann was finally diagnosed by Northwestern doctors with REM sleep behavior disorder in 2008. They gave him clonazepam, which worked like a charm, while also treating a mild case of sleep apnea, which can contribute to REM behavior disorder episodes.

"It was the first time in more than 16 years that I could say I got a good night's sleep," Neumann said. "I sleep really well now."