There are many types of headache but by far the commonest is tension headache.This originates in the upper neck due to a mechanical dysfunction. Tension headache can be caused by cervical spondylosis, arthritis, poor posture and a bad neck position whilst sitting at the computer. Sleeping on the stomach or using an inadequate pillow could also cause a tension headache. Swimming breaststroke with neck extended can trigger headaches too.
Pain usually starts at the base of the skull and spreads to the forehead, temple and sometimes the eye.