A headache in which pain originates behind or around one eye and generally awakens the individual from sleep; pain may radiate into the temple, jaw, nose, teeth, or chin; the eyelid droops, the eye tears, the face flushes, and the nose congests; causes excruciating pain. Individual headaches last 15 minutes to 3 hours but tend to “cluster”, occurring up to several times per day for periods of about 1 to 16 weeks and then not again for months or years.