Tension headache
Cluster headache
Migraine
Trigeminal neuralgia
Meningitis
Temporal arteritis
* Very sudden onset
Subarachnoid haemorrhage
Raised intracranial pressure (tumour, hypertension, hydrocephalus)
* History of hypercoagulability
Venous sinus thrombosis
Acute closed-angle glaucoma
Sinusitis
Carotid artery dissection