The patient wakes up with a sudden headache in the middle of the night, which means that the headache is severe. It is recommended that the patient immediately consult a hospital because there may be several causes of severe headache: 1. It may be caused by cerebral vascular rupture or hemorrhage, such as subarachnoid hemorrhage, which can lead to severe headache with increased intracranial pressure. The patient may have nausea, vomiting, and cervical tonicity, which require active treatment because of the high lethality of subarachnoid hemorrhage. 2. The sudden headache in the middle of the night may be a cluster headache attack if the patient does not have symptoms of neurological deficits or cervical tonicity. If the patient’s headache is on one side, accompanied by tearing of one eye, conjunctival congestion, nasal congestion or redness of the head and face, it is considered a cluster headache attack, which also requires a visit to the hospital for symptomatic pain relief treatment.