Panic attacks are suden, discrete periods of intense anxiety, mounting physiological arousal, fear, stomach problems (spastic colon) and discomfort that are associated with a variety of somatic and cognitive symptoms. The onset of these episodes is typically abrupt, and may have no obvious triggers. Although these episodes may appear random, they are a subset of an evolutionary response commonly referred to as fight or flight that occur out of context. This response floods the body with hormones, particularly epinephrine (adrenaline), that aid in defending itself from harm. Experiencing a panic attack is said to be one of the most intensely frightening, upsetting and uncomfortable experiences of a person's life.