Cluster headache (CH) always involves pain that is one sided (although it can switch sides) and the main defining feature is the association with one or more of the 'cranial autonomic' features normally described as follows:
• Reddening and tearing of the eye • A runny or blocked nostril • Droopy eyelid • Constriction of the pupil • Flushing and facial sweating There is, as yet, no known cause for cluster headache. However, cluster headache has two major clinical features: the trigeminal (nerve) distribution of pain and the associated ipsilateral (same-sided) autonomic symptoms."
Source Organisation for the Understanding of Cluster Headache based at UK's Royal Free Hospital and King's College Hospital.
Also see: Migraineplugin-autotooltip__plain plugin-autotooltip_bigMigraine
"Chronic migraine has a great detrimental influence on a patient’s life, with a severe impact on socioeconomic functioning and quality of life. Chronic migraine affects 1–2% of the general population, and about 8% of patients with migraine; it usually develops from episodic migraine at an annual conversion rate of about 3%."