The causes of severe headache are generally divided into two categories: first, functional headache, of which vasoneurotic headache is the main representative, also called migraine, which occurs due to the dysfunction of vasoconstriction and dilation of intracranial blood vessels, or the abnormal secretion of neurotransmitters such as 5-hydroxytryptamine and trigeminal nerve dysfunction. In addition, there are also primary trigeminal neuralgia and occipital neuralgia, both of which are severe headaches whose causes are not yet completely clear. The second type of severe headaches caused by organic diseases, the most representative ones are subarachnoid hemorrhage and ventricular hemorrhage. Substantial intracerebral hemorrhage can also cause severe headaches, but the pain level is usually less than that of subarachnoid hemorrhage. In addition, central nervous system infections such as viral meningitis, tuberculous meningoencephalitis, and septic meningitis can also cause severe headaches.