女性,23岁。发作性头痛、呕吐4年。每月发作1~2次,均于月经前发作。神经系统无阳性体征发现。下列发病机制中哪项对本患者起主导作用()
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
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