A sudden increase in pain that may occur in patients who already have chronic pain from cancer, arthritis, fibromyalgia, or other conditions. Breakthrough pain usually lasts for a short time. During breakthrough pain, 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. Breakthrough pain 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. Breakthrough pain is usually not a symptom of a new condition or a condition that has gotten worse. Also called pain flare.