Sex is also a pain reliever, ten times more effective than Valium: immediately before orgasm, levels of the hormone oxytocin rise by five times, determining a huge release of endorphins. These chemicals calm pain, from a minor headache to arthritis or migraines, and with no secondary effects. Migraines also disappear because the pressure in the brain's blood vessels is lowered while we have sex. So now we see that actually, a woman's headache is rather a good reason for having sex, not against it.
Info Source: By Stefan Anitei, Science Editor of 'Softpedia'