Sudden onset, severe “thunderclap” headache
Subarachnoid hemorrhage
Headache onset with exercise
Ruptured aneurysm
New headache onset after age 50
Temporal arteritis, intracranial mass
Headache with fever, stiff neck, photophobia, systemic signs
Meningitis, encephalitis
Headache with focal neurologic signs, symptoms, or papilledema
Tumor, subdural hematoma, epidural bleed
Multiple people with similar new onset headache, i.e. family coworkers
Environmental exposure, CO poisoning.