The great researcher Ahmad ibn Muhammad, popularly known as Ibn Maskawayh, in his bookTaharat al-Araq writes something which can be summarized as follows: Anger, in fact, is an inner psychic movement due to which a state of agitation is produced in the heart's blood, arousing a desire for vengeance. When this agitation becomes more violent, it intensifies the fire of anger. A violent commotion in the blood seizes the heart, filling the arteries and the brain with a flurry of dark smoke, on account of which the mind and the intellect lose control and become powerless. At that time, as the Hukama (wise ones) maintain, the inner state of the person resembles a cave where fire has broken out, filling it with flames and suffocating clouds of smoke that leap out of its mouth with intense heat and a fiery howl. When that happens, it becomes extremely difficult to pacify such a person and to extinguish the fire of his rage; whatever is thrown in it to cool it down becomes a part of it, adding to its intensity. It is for this reason that such a man becomes blinded to propriety and deaf to guidance. In such a condition, there is no hope for him.
Anger causes a bodily reaction; the sympathetic nervous system and muscles mobilize for physical attack. Muscles tense and the blood pressure and heart rate skyrocket. Digestive processes stop. Certain brain centers are triggered, which then change the brain chemistry. When angry, the bodily functions change for the worse.
A quote just came up to my mind: "Though you may feel justified at your anger; Beware! It may rise up to destroy us."
Book referenced in the following article (an article on the reality of anger):