A character who is undergoing changes of personality (like buying off mental disadvantages - flaws - or changing alignment) might confront personifications of aspects of his personality in dreams: a griffon representing the courage he needs to face a terrible foe, or a satyr standing for the lecherousness a warrior must overcome to be admitted to an order of knights who must uphold vows of chastity.
When was the last time a character caught a cold or flu? Real people get them every now and again even with solid heating and dry interiors. Your characters are out in the cold and wet, and even inside is not always dry and warm. Imagine having to stop your dungeon crawl, sitting in a tight defensive position, while you all are feverish.