So Table 72 in the core book (not the Core Exxet as I don't have a copy of it) has pretty decent rules as far as resisting Diseases goes but I am unsure how to decide which disease stands at what what DR resist. Like Would the Flu be a DR 20, 40 or what? Also how would you rule on things like Hypothermia which are more of a physiological reaction as opposed to an actual disease? Would you simply call it a Physical Resistance and call it a day? Any help you all can give would be highly appreciated.

Apparently the gravity of a disease is up to the GM to decide since there is no example in the books unlike poisons. And concerning hypothermia there isn't any precise rule either but I think you can make up something with the rules for frost damage and frost intensity (chapter 14 of the core book).