<s>[INST] A 37-year-old man, previously healthy, presents to the emergency department with complaints of severe headache, nausea, and vomiting. He also reports photophobia and phonophobia. His symptoms started suddenly and have been ongoing for the past 4 hours. A comprehensive physical examination is performed, and his vital signs are stable. He has no significant medical history, and his only current medication is an occasional use of acetaminophen for headaches.

What is the most likely diagnosis for this patient's condition?[/INST]