What causes a sudden headache behind the eyes?

A sudden headache behind the eyes can have several causes. Tension headaches are the most common, triggered by stress, poor posture, or eye strain from screens. Cluster headaches cause severe, stabbing pain around or behind one eye and occur in cyclical patterns. Sinusitis creates pressure and pain behind the eyes due to inflamed sinus cavities. Migraines often produce throbbing pain that can concentrate behind the eyes, sometimes with visual disturbances. More serious causes include increased intracranial pressure, optic neuritis, or a sudden severe "thunderclap" headache, which can signal a brain aneurysm and requires immediate emergency care. Vision problems like uncorrected refractive errors can also cause eye strain headaches. Persistent or severe cases should be evaluated by a doctor.