A35-year-old man complained of a sudden onset of severe headache. For thepast two weeks, he woke up around 3：00 a.m. due to soreness behind the lefteye. His pain continued for about an hour. Today, he visited the emergencydepartment at 5：30 a.m.His consciousness was clear, but he appeared restless. His body temperaturewas 36.4 ℃. Pulse rate was 84/min. Blood pressure was 136/80mmHg.Conjunctival hyperemia and tearing of the left eye were observed. There wereno meningeal signs. MRI and MRA of the head showed no abnormalities.What is the most likely diagnosis?