I'll just deal with disease. Mediaeval doctors saw illness as the product of internal imbalance rather than external agents like we do. The human body had four humours: blood, yellow bile, black bile and phlegm. An excess of any of these caused illness. Treatment should suppress the excessive humour so if a person had a bronchial infection this was probably due to excessive phlegm which was cold and moist. The patient would be given foods which promoted hot, dry humours and should avoid cold, wet things.

Source: Nancy G. Siraisi, Mediaeval and early Renaissance Medicine