According to my 1916 medical dictionary, with a little help from "Ask Yahoo":
Consumption is an old name for tuberculosis (TB) that describes how the illness wastes away or consumes its victims. TB is "an ancient enemy" that has plagued humankind for more than five thousand years. The Greeks called it phthisis, and Hippocrates advised his medical students against treating it, because it was almost always deadly, and a dead patient was bad for business.
For "debility," the dictionary says "lack or loss of strength." So that is in reality a symptom and not a diagnosis- it could be caused by any number of things.