Anthony Robbin’s Unlimited Power describes a case of a psychiatric patient with a split personality. One of her personalities was diabetic, while another was not. Her blood sugars would be normal when she was in her non-diabetic personality, but then when she shifted into her diabetic alter ego, her blood sugars rose, and all medical evidence demonstrated that she was diabetic. When her personality flipped back to the non-diabetic counterpart, her blood sugars normalized.
Psychiatrist Bennett Braun, author of The Treatment of Multiple Personality Disorder, describes the case of Timmy, who also had multiple personalities. One personality was allergic to orange juice, and when this personality drank orange juice, Timmy would break into blistering hives. However, another personality was able to drink orange juice uneventfully. If the allergic personality was in the midst of an allergy attack and he shifted back to the non-allergic personality, the hives would disappear instantly.