My wife has an autoimmune disease (one of the bad, insidious ones) and uses it because it's simply common parlance among people with autoimmune diseases. Not idiotic at all and it's no different than slang in any other niche or subculture, though it is idiotic that fat people are using it. Despite having the holy grail of condishuns, shes a shitlord and accordingly works out hard, counts calories, and stays lean, fit, and able to live her life unimpeded and without being on a drug cocktail. Unfortunately most people with her disease miss this and go straight for the pills and sofa. She's basically reversed her symptoms.  The sad thing is she was raised by a stereotypically lazy hamplanet and we both conjecture that being in a pressure cooker of environmental and mental garbage may have been what wrecked her immune system enough for this to happen. She hates everything her upbringing represents and refuses to go down that route.