A 35-year-old man complained of a sudden onset of severe headache. For the past two weeks, he woke up around 3：00 a.m. due to soreness behind the left eye. His pain continued for about an hour. Today, he visited the emergency department at 5：30 a.m.

His consciousness was clear, but he appeared restless. His body temperature was 36.4 ℃. Pulse rate was 84/min. Blood pressure was 136/80 mmHg.Conjunctival hyperemia and tearing of the left eye were observed. There were no meningeal signs. MRI and MRA of the head showed no abnormalities.

What is the most likely diagnosis?