You ought not to attempt to cure the eyes
Without head,
Or head without body,
So you should not treat body
Without soul."

-from The Sustainable Herbalist;
The Sustainable Life

by Candis Hope Kirjales

Not even he could have imagined that so many different causes have been found for headache.

Here are just a few that may need to be considered when someone presents with new onset headache:

Brain Abscess
Sinusitis
Stroke, Hemorrhagic
Encephalitis
Stroke, Ischemic
Glaucoma, Acute Angle-Closure
Subarachnoid Hemorrhage
Headache, Cluster
Subdural Hematoma
Headache, Migraine
Temporal Arteritis
Meningitis
Temporomandibular Joint Syndrome
Otitis Media
Trigeminal Neuralgia
Fever
Anoxia
Cervical spondylosis
Tumor
Caffeine dependency
Nonprescription analgesic dependency
Severe anemia or polycythemia
Uremia
Hepatic disorders
Toxic effects from drugs or fumes (carbon monoxide)
Dental disease
Paget disease of bone
Refractive error
Hypertension
Hypoxia
Lesions of the eye or middle ear
Lesions of the oral cavity

Even for a partial list, that's pretty daunting - and a good reason to get checked out by a qualified practitioner, even for something deceptively simple-sounding like "headache", if it's a new problem.