A 25-year-old woman reports recurrent episodes of severe headache, typically affecting one side of her head, described as pulsating or throbbing. The headaches usually last between 6 and 12 hours and are associated with nausea and increased sensitivity to light and sound. Importantly, about 20 minutes before the headache starts, she experiences flashing lights and zig-zag lines in her vision that resolve as the headache begins. What is the most likely diagnosis?