A 35-year-old man presents with daily headache. He describes two attacks per day over the last 3 weeks. Each attack lasts about an hour and awakens him from sleep. The patient has noticed associated tearingand reddening of the right eye as well as nasal stuffness. The pain's deep, excruciating, and limiting to the right side of the head. The neurological examination is normal. What is the most likely diagnosis ?