Jeff, a 22-year-old Filipino-American, steers a tank through the Iraqi desert. It's hot, too hot to touch the frying-pan metal walls of the tank for more than a second. The smell of diesel fuel seeps through the air.

Something breaks the desert's monotony: a dark shape on the horizon. It looks a mirage ... but it's moving. "Do you see that?" Jeff asks the other three soldiers riding with him. They nod.

The soldiers draw nearer and realize it's an Iraqi tank. "Let's turn around," says a sergeant, who stands up through a hatch, scanning the distance. "We gotta go, we gotta move."

"No, we're pushing forward," Jeff argues. "There's only one of them. We've got the guns." The two argue for a while and finally decide to keep moving.

They get closer. All of a sudden, five or six Iraqi tanks appear over the horizon. The Americans are outnumbered. "Oh, shit," Jeff mutters.

There's a flash at the Iraqi tank's barrel.

"Open fire!" shouts the sergeant. Bullets rain down on them. Jeff tries to steer, but the wheels won't move—enemy fire had destroyed the engine.

The soldiers jump out their doors and regroup behind their tank. Jeff realizes there's only three of them; someone's missing. He runs a few steps and sees the sergeant slumped over the tank's roof, covered in blood.

Jeff wakes up in a cold sweat, heart pounding. He looks around his Brooklyn bedroom, trying to remember where he is. He's 32, not 22. It's been a decade since he was a scout in the army, and this scene is just a dream built from memories.

He's been getting this nightmare a lot lately, but that's not unusual. He gets combat nightmares pretty often, up to two or three times a week when he's stressed. Sometimes, he wakes up to find he can't move, and he feels like someone, or something, is trying to drag him out of his bed.

It's not unusual for veterans to have sleep problems after their service. In fact, according to Colonel Vincent Mysliwiec, a sleep-medicine specialist for the U.S. Army, it’s become increasingly common since 2006, due to the conflicts in Iraq and Afghanistan.

Traditionally, soldiers experiencing this sort of thing are diagnosed with post-traumatic stress disorder (PTSD) or a more traditional sleep disorder. But a recent study suggests some of them may have a new affliction: trauma-associated sleep disorder (TSD).

People dealing with TSD have vivid nightmares and a myriad of other sleep problems, including insomnia, anxiety, night sweats, thrashing, screaming, kicking, and punching while asleep. They often act out their terrifying dreams.

This can get extreme. Some soldiers wake up from nightmares about pummeling the enemy to find they've hurt their bed partners. One study participant came in after his wife woke up with bruising and a black eye, explaining that he started screaming and attacking the wall while asleep. When she tried to stop him, he starting hitting her.

“She got caught in the crossfire,” he said.

Doctors observed symptoms like this during the Vietnam War, but they were too focused on PTSD at the time to consider another classification, according to Mysliwiec. But TSD is different than PTSD: half of TSD sufferers don't have daytime PTSD symptoms such as flashbacks and severe emotional reactions to things that remind veterans of traumatic events. Doctors also sometimes attribute the symptoms to REM behavior disorder, a degenerative brain disease. But active young men rarely get REM behavior disorder. Nor do TSD sufferers fit the criteria for nightmare disorder, since people who just have nightmares don't typically move while they're dreaming.

"We knew [veterans] developed insomnia and sleep apnea, but we've never seen a truly unique sleep disorder related to a traumatic experience," says Dr. Mysliwiec, who headed the study.

Mysliwiec started to think about the possibility of an entirely separate disorder when he monitored a patient who screamed and yelled in his sleep. Even though complaints about sleeping issues are common among veterans, Mysliwiec thinks this may be the first time someone has observed this in a lab. It's hard for scientists to catch; veterans know labs are monitored, and they may feel safer in them, making it less likely they'll have these violent nightmares.

Mysliwiec and his colleagues realized this might be a unique problem, and they organized a study. They found four young, male, active-duty soldiers who complained of sleep problems like throwing pillows, punching walls, and cursing while asleep. One once woke up and found himself choking his wife. (She wasn’t hurt badly, but she started sleeping in a different bed for safety.)

The researchers watched the soldiers fall asleep and act out their nightmares, yelling and fighting in their sleep. One screamed, "Oh fuck, leave me alone!" The researchers published their findings in the Journal of Clinical Sleep Medicine in October, and called for TSD to be recognized as a new diagnosis.

Soldiers usually don't sleep well in combat zones; they are often on edge, ready for emergencies. When they come home, it can be hard to transition back to regular, stress-free sleep. Some dream of past combat and act out their nightmares, even though the human body normally paralyzes itself for safety while the brain dreams. Mysliwiec theorizes that, with TSD, the sufferer’s intense stress overrides this natural paralysis.

Mysliwiec says the drug Parazin helped a lot of his patients by blocking the nervous system rush that makes them fight in their sleep. Once treated, one of the soldiers in the study was able to go back to sleeping in bed with his wife.

It’s pretty common for soldiers who have seen combat to have nightmares, but for those like the men in the study who experience more serious symptoms, many unfortunately don't seek help. They may feel guilty and ashamed about what they do while asleep. And as a result, a lot of veterans only see doctors after their spouses make them, Mysliwiec says. That's why Mysliwiec thinks this diagnosis is so important: Once you put a name on something, people can recognize it in themselves and others. Doctors can study it, and sufferers can get help.

But for the masses of still-untreated veterans, the stress of sleep problems bleeds into everyday life.

"I wish I knew which ones were the memories and which were the dreams," says Jeff. "Sometimes, I don't know."