Migraine 

Migraine

From the Globe and Mail Friday: migraine headaches are probably under-reported because people don't recognize the symptoms--they can be mistaken for ordinary tension headaches, or for sinus headaches, and they are likely to be mistreated in either case.

"Migraine headaches are often referred to as an invisible epidemic. They are the leading cause of absenteeism in the workplace."

I would also guess that people, maybe especially men, are unwilling to admit at work that they suffer from frequent headaches.

It strikes me that this, even more than say mental illness, points to some problem in the adaptation of human beings to our environment. Why so many disabling headaches? Do other primates get them?