A sudden increase in pain that may occur in patients who already have chronic pain from cancer, arthritis, fibromyalgia, or other conditions. A pain flare usually lasts for a short time. During a pain flare, the level of pain may be severe but the type of pain and where it is in the body are usually the same as the patient’s chronic pain. Pain flares may occur with stress, illness, and certain activities, such as exercising or coughing, or when the dose of pain medicine that the patient is taking wears off. Pain flares are usually not a symptom of a new condition or a condition that has gotten worse. Also called breakthrough pain.