A cluster headache attack is a dramatic event. The pain usually peaks in a few minutes, but attacks can last from 5 minutes to 3 hours and can occur from once every other day to 8 times a day. Unlike migraine headaches, cluster headaches are not preceded by auras (visual or other types of sensory disturbance), so people usually have little or no warning that one is about to happen. A unique feature of cluster headaches is that they often begin while a person is sleeping. The pain and location of cluster headaches are its most important defining features. The pain is generally described as excruciating, explosive, deep, and/or piercing (but usually not throbbing). Some people say that it feels as if an ice pick were being driven into their eye. This stabbing eye pain may feel like an electric shock, which may last for a few seconds, followed by a deeper element that continues for a half hour or longer. The pain almost always begins in or around an eye and always on one side of the face. For most people, the pain stays on the same side of the face from one cluster headache to another, while in a small minority, the pain switches from side to side from one headache to the next. The pain may spread to other parts of the face and neck but usually remains centered around one of the eyes. A person experiencing a cluster headache may be very restless. Some people bang their head against a hard surface or sit, rock, or pace. Cluster headaches are often associated with the following physical signs and symptoms: Ipsilateral nasal congestion and rhinorrhea (stuffy and runny nose on the same side as the pain around the eye) Lacrimation (watery, tearing eyes) Conjunctival hyperemia (increased blood flow to the membranes lining the eyeball and the inside of the lids) Facial diaphoresis (sweaty face) Palpebral edema (swollen eyelids) Complete or partial Horner syndrome (a condition causing ptosis [eyelid closure], change in pupil size on one side of the face, and lack of sweating) that may persist between attacks Tachycardia (fast heartbeat) Between attacks, people with cluster headaches usually have normal physical examination findings.