Why cluster headache affects one side

An attack may cause piercing or burning pain around one eye, the temple or forehead. The eye can water or redden, while the eyelid may droop or swell; the nostril may block or run on the painful side. The pattern can recur on the same side during a period of attacks, although the side may differ between separate periods.

One-sided headache is not unique to cluster headache. Migraine, nerve pain, eye disease and other conditions can also affect one side. The speed of onset, duration, associated signs and examination help distinguish them.

Keep a simple diary showing the painful side, exact starting point, attack timing, eye and nose changes, restlessness, possible triggers and medicines taken. Stay in a safe place while the pain is severe and avoid driving if vision or concentration is affected. Arrange a GP consultation to discuss a confirmed diagnosis and a treatment plan for attacks and prevention.

Seek emergency care for a sudden worst-ever headache, weakness or numbness, speech trouble, confusion, fainting, seizure, fever with a stiff neck, or new loss of vision. Get urgent assessment for a painful red eye, unequal pupils or a headache after injury. A new one-sided headache also deserves medical review, even when it resembles a previous episode.

Do my one-sided symptoms match cluster headache? Could an eye or nerve problem explain them? What should I do at the first sign of an attack? When should I use emergency services rather than wait for an appointment?