Easily one of the most common afflictions, headaches strike nearly everyone at some time. Although many of these spells are transitory, experts estimate that up to 90 percent of all people - as many as 50 million in the United States alone - suffer some form of recurrent or chronic headache in their lifetime. These attacks are often severe enough to disrupt daily life. An estimated 8 million people visit their doctors each year with headache complaints. The cost, in terms of lost productivity and diminished quality of life, may be beyond any ability to compute.