In medicine, the traditional meaning is that of a rapid loss of fever and return to comparative health in certain acute diseases. For example, PNEUMONIA, in the pre-antibiotic days when allowed to run its natural course, ended by crisis usually on the eighth day, the temperature falling in 24 hours to normal, the pulse and breathing becoming slow and regular and the patient passing from a partly delirious state into natural sleep. In this sense of the word, the opposite of crisis is lysis: for example, in TYPHOID FEVER, where the patient slowly improves during a period of a week or more, without any sudden change. A current use of the word crisis, and still more frequently of critical, is to signify a dangerous state of illness in which it is uncertain whether the sufferer will recover or not.