The healing crisis. In Arabic: al-bahraan. It is, "the sudden change in the condition of the patient suffering from acute fever, which is usually accompanied by excessive sweating and rapid decrease in temperature. The abnormal heat of fever acts on the maturing of the superfluous matters so that they can be dealt with by the body. It is also described as a detoxification process.” Ibn Sina, as quoted in “Avicenna’s Medicine”.
“Crisis in terms of substance repulsed, has five modes: vomiting, diarrhoea, nosebleeding, urination, and perspiration. Crisis by urine or perspiration is incomplete because a thin substance is thrown out and a thick one remains. Crisis by vomiting, nosebleeding, or diarrhoea is complete.” (Robert Thomson, in “The Grosset Encyclopedia of Natural Medicine” (1980))
It is, as they say, a Good Thing.