What can cause a grown man to groan out loud, rock back and forth on the floor, dig his hands into the carpet, cradle his head or crawl on his knees?
The answer is a cluster headache, rare, intensive kind of pain that affects about 1 million Americans — 90 percent of them male — according to the National Headache Foundation.
The headaches are so named because they occur in "groups" or clusters, several times a day for several weeks before they subside. Months later, they start all over again.
Taking two aspirin and waiting will not help, says ABCNEWS Medical Correspondent Dr. Nancy Snyderman.
The prevailing explanation for cluster and migraine headaches is that dilation of blood vessels causes the pain. Doctors use oxygen to treat the condition, because it constricts brain blood vessels; researchers are looking at the role of the hypothalamus in the brain.
Like a 'Hot Poker in Your Eye'
Those who suffer from cluster headaches say there's nothing mild about them.
"It feels like you have a hot poker stuck in your eye," says Pat Kelly, a cluster headache sufferer.
"I've had broken bones and burns and I've had nothing compared to it," said Dan Skopek, who got his first cluster headache 10 years ago at age 21.
Though doctors don't know why, men are affected more often than women. Smoking and drinking are notorious headache triggers.
Most cluster headaches have a seasonal rhythm, occurring most often in the fall or the spring.
But up to 20 percent of sufferers have chronic cluster headaches, every day.
"Patients will often cry or scream or pace or pound their heads or their fists against the wall," says Dr. Joel Saper, a neurologist from the Michigan Head-Pain and Neurological Institute. "It's a devastating experience, a torturing experience."
Patients and doctors call them suicide headaches.
Dr. Seymour Diamond, of the Diamond Headache Clinic in Chicago, says he has seen cases go to extremes: "The only suicides I've ever seen in any headache patients have been men who have had clusters."
Cluster headache sufferers feel compelled to move around, bang their heads and cry out. Migraine headache patients typically seek a quiet dark room to lie down in. An individual cluster headache lasts 45 minutes to two hours, while migraines can go on for several days.
"You beat your head on the wall, on the floor, because that feels better than the headache," Skopek says. "If the doctors told me that it was my arm that was causing the headaches and I had to have it amputated I would have done it in a second."
After being misdiagnosed and overmedicated, Skopek says he was ready to bid his wife and children goodbye and commit suicide.
Pass the Oxygen
But that was before Skopek found help at the Michigan Head-Pain and Neurological Institute.
While there is no cure for cluster headaches, a combination of drugs can usually bring them under control. Some drugs are preventive, stopping headaches before they happen, and others are abortive, stopping headaches in progress.
Pure oxygen is the most popular treatment for stopping headaches and it is safer than others, which can have powerful side effects, Snyderman says.
Skopek keeps tanks in his house and his car, sometimes stopping by the side of the road to take a hit so he can keep working.
Kelly, whose headaches mostly occur at night, also has a routine he follows when headaches strike: his chair, his oxygen, and a silent TV to stare at until the pain subsides.
Some doctors prescribe antihistamines to stop cluster headaches, but Diamond believes that histamine itself can stop the pain and has tried treating patients with histamine infusions.
Kelly swears by the histamine drip: "I don't mind putting in 12 days in the hospital if it will give me nine or 10 months headache-free," he says.
The newest research points to a structure deep in the brain, the hypothalamus, which is involved in pain perception, the body's cycles and pain perception. That may explain why different drugs used to treat clusters all work, despite their different actions.
But all the research matters a lot less to Skopek, who is pleased to at least be able to control, if not eliminate, his pain.
"I look forward to just growing up now with my family… my kids, my wife," Skopek says.