Attacks typically last from 15 minutes to 3 or more hours. Onset is rapid and can wake people from sleep. There are no warning signs, but some people have preliminary sensations of pain ("shadows") in the general area of the attack. Associated symptoms occur on the same side of the face as the headache and can include tearing, eye redness, runny nose, facial sweating, and drooping eyelid. Patients also have a sense of restlessness. Headaches typically occur at the same time each day or night, suggesting that the hypothalamus (the part of the brain governing "circadian rhythm") is involved. In episodic cluster headache, attacks often occur daily for several weeks, separated by a headache-free period lasting several weeks, months, or years. About 10% to 15% of individuals with cluster headaches have chronic cluster headaches. These patients can have multiple headaches daily for years without any remission between cycles. Cluster headache is much less common than either migraine or tension-type headaches.