Not tonight, honey. I'm going to have a headache." For many, that variation on the old joke isn't funny. They suffer from sex-related headaches, a painful malady that can cool even the hottest passion.
"They're severe and they come on fast and they stop you in your tracks," says Dr David Haas, a professor of neurology at the State University of New York Upstate Medical University in Syracuse. "They're no fun. They hurt a lot."
Despite continuing research, there's no consensus on what causes sex-related headaches. But many who suffer them also are prone to other types of headaches, such as migraines or exertion-related headaches.
But if the cause of these headaches remains uncertain, there's no doubt about the result.
Often described as "a thunderclap," the headache frequently appears in the base of the skull at or near the moment of orgasm, transforming pleasure to pain in seconds. Intense pain may last for 10 to 15 minutes, with lesser pain lingering for another hour or two.
Sex-related headaches are sometimes referred to as "coital headaches," but that's not exactly accurate, Haas says, since they can occur even during solo sex.
"You can get it with masturbation," says Haas, who runs a Web site devoted to headaches. "I [treated] a woman professor who would get the headache with masturbation more than with intercourse."
Men suffer disproportionately
Men are far more likely to suffer sex-related headaches than women, with most authorities saying men account for about 80 percent of the cases. Again, there's little consensus on why men suffer disproportionately.
One theory, however, claims that, for women, vaginal stimulation may help block pain, as a way of preparing them for childbirth.
The effects of sex-related headaches go beyond pain, however. Even though most sufferers can be treated successfully, they may develop a lingering fear of sex.
"You're talking about something that's a physiological event that has a lot of psychological impact, too," says Jeanetta Rains, clinical director of the Centre for Sleep Evaluation in Manchester.
"It's a powerful event to have happen to you," says Rains, a psychologist who has done a decade's worth of research on sleep and headaches. "It's certainly something that can provoke a lot of fear. They may worry they can never have sex again."
But Rains says almost all cases of sex-related headaches can be successfully managed. The first step is a brief period of abstinence from sex - perhaps for a couple of weeks.
"It's best not to get right back on the horse," she says.
People can vary their sexual positions, trying more passive approaches to cut down on sexual exertion, Rains says. And anything that improves general health - such as losing weight, lowering blood pressure, improving cardiovascular strength - is likely to help the headaches, as well.
Some drugs can be helpful, such as propranolol or endomethicin. Even ibuprofen, a common over-the-counter headache remedy, has proven successful.
Some non-medical treatments effective
Dr Seymour Diamond, executive director of the National Headache Foundation, says he sometimes suggests non-medical treatments, such as biofeedback or relaxation therapy.
But Diamond says anyone who has a recurring sexual headache should see a doctor to rule out more dangerous problems, such as aneurysms or tumours.
"I would suggest, if anybody has this complaint, they should not be afraid to tell their doctor about it," says Diamond, who also serves as director of the Diamond Headache Clinic.
"I think the greater concern is that their doctor might not take it seriously," he says. "A woman may mention to her gynaecologist that she gets a headache during sex, and he may say, 'Oh, that's nothing.' "
"Someone has a headache," he says. "They don't have sex for a week or two, and it goes away, so they don't tell their doctor. So it may be more common than we know."
Doctors say a brief, isolated incident is probably no cause for alarm. But if the headache lasts for more than an hour or two at high intensity, you should have it checked out.
"It's an extremely interesting curiosity," says Haas. "The medical science of headache is in its infancy."
"It's difficult to get at," he says. "Everything happens in this closed box, the skull, with 20 to 40 billion neurons. It's a very complex machine."
"We really don't know what's going on in the brain," Haas says.