A fibromyalgia flare is a temporary increase in the number and/or intensity of symptoms. Some flares only last for a day or two but others may continue for several weeks or even months. The best way to prevent fibromyalgia flares is to identify what causes them and, when possible, try to avoid the circumstances that trigger them. Keep in mind that a flare may not occur for up to 48 hours after the event that triggered it. Following are 10 common causes of fibromyalgia flares.