recurrent clusters of sudden onset lancinating retro-orbital headaches lasting minutes to 3 hours usually occurring in the early hours of the morning (perhaps REM sleep mediated) causing the patient to become agitated, restless and walk around
historically mainly adult males who smoke heavily and have high alcohol intake but becoming more widely recognised in women as well with gender ratio now around 2:1 rather than historic 6:1 ratio
usually associated with one or more features of ipsilateral Horner's syndrome