JFK is said to have had Addison's Disease, but Dr Steven Rochlitz book on Porphyria reveals that JFK was diagnosed by his White House physician, Dr Janet Travel as having episodic adrenal failure for unknown reason and that he did not have Addison's.

Dr Rochlitz new 3rd edition of his book, Porphyria: The Ultimate Cause... examines JFK's entire medical history of episodic adrenal [partial] failure as well as his life-long chronic pain, GI, immune, allergy, asthma, neurological, muscular, bladder and other complaints and asserted that JFK had porphyria his whole life.

Porphyria is a common, not rare, disease and a frequent cause of adrenal and/or thyroid weakness.
You can find a good youtube interview on porphyria here:

https://www.youtube.com/watch?v=UVEjVxx2nc8&feature=youtu.be

Adrenal problems can go away if porphyria is dealt with.