What is the physiological reason people get headaches?

Oversize question!: The physiological reasons are far too numerous to cover in less than a huge book. Causes can be hormonal, water retention, aneurysms or anything that stretches the meninges, tumors, high blood pressure (stretching blood vessels), and many mechanical reasons incl muscle tension, etc.A good osteopathic dr can, via a full history & physical, incl. Hands-on exam, help determine cause & potential fixes.