What are some chronic illnesses that can only occur in a fantasy setting?
Partial transformation - mummy rot is slowly turning you to sand, a near miss from a medusa left you with partially stoned body parts, etc.
Hypnotic suggestions from being mind controlled persist after the controller’s death, causing the victim to occasionally take actions to support the cause of a mind flayer cult that no longer exists.
Repeated demonic possession has left the patient with permanent gaps in their soul’s defenses, causing them to immediately get re-possessed if they go outside a consecrated area.
Post-resurrection trauma as the revived soul remembers an unpleasant afterlife.
Magical healing can get very weird if something is stuck in the wound. It’ll get you back on your feet, but you can get outcomes like “there’s a chunk of wood fused into your chest because the magic couldn’t figure out how to get the arrow out of your chest and just healed it in place,” and this can cause mobility issues or infection vectors down the line.
Magical “allergies” - casters can develop sensitivity to a certain kind of magic, e.g. they’re fine with transmutations, but conjurations cause them to magically “sneeze” and involuntarily vanish parts of whatever they just conjured, or randomly change the color of their hair, or duplicate their conjured items. Quite distressing when you wanted to conjure a fire to warm your party on a cold night, but now you’ve started a forest fire, sneezed half of it back out, and your hair is green polka dots.
Magical reactivation, as shingles is to chicken pox. Victims of a Sleeping curse early in life may find that later in life the spell reactivates in new variant forms. Normal sleep may result in accelerated growth of nearby plant life, narcolepsy in persons occupying the same building, weakening of the dream-reality barrier, or painful bedsores.
