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.
SHealth tied to something else - the health of a tree, the amount of frost on the ground, the inverse of another person’s, the political power of whoever cursed you
Curse of bad luck - makes any small illness or injury potentially fatal if not treated with anti-curse in addition to anti-infection procedures
Magical reliance on a magical or nonmagical substance - can have any number of side effects
Repeatedly being drunk by vampires can cause an increase in blood production and therefore high blood pressure and related ailments. Can be treated by blood letting.
There’s a lot of hybridization happening in a lot of fantasy settings, and that’s just asking for a lot of people with weird half-dragon genetic disorders. Works out fine for some people, not so much for others.
Parasitized by (insert creature here). If you don’t take the correct precautions to keep it dormant it will continue to spread and eventually hatch out/transform you.
Repeated contact with the undead has left you open to their influence - leading to hearing or seeing things that other mortals can’t, which can distort or distract from more mundane concerns.
Alternately to being more vulnerable to intrusion, one’s soul can form a scar that makes helpful magic more difficult to take in.
Sleep disorders that make one fall into an impenetrable sleep at a specific trigger, or to do so for years at a time.
Out of phase with 4D space, one’s body not connected to itself or anchored in place/time in the usual way. There could be a consistent two hour gap between the things you hear and what has happened, you might clip into the floor as if it was in a different place for you, or you might slide through the material plane in cross section.
Intermittent intangibility.
Split into two people, each with only half your traits.
Stuck in a mirror.
Sensitivity to ambient magic - like the thing where peoples’ joints ache before a storm but for being near ley lines or people with a lot of magic built up or other magic reservoirs. - The potential for magic, but where the magic has not yet begun.
Heal spell dependency: years of repeated serious injuries being healed by magic causes the body to stop healing naturally. seen often in professional fighters and those with a long career in hazardous occupations.
the forgotten dread: memory modification magic has caused the subject’s conscious mind to forget some past trauma, but their subconscious still remembers, causing them emotions that they cannot explain or justify ranging from mild discomfort to blind panic when presented with triggers related to the aforementioned trauma. often encountered in cases where the subject has paid an unscrupulous mage to make them forget their past as an ill-advised alternative to therapy.
Psychically Transmitted Memories: the subject’s mind has been linked to another person’s and, although the bond has since been severed, they have retained memories or thought patterns from the other person that are difficult to distinguish from their own.
Negative Life Syndrome (previously “False Life Syndrome”): seen most often in cases when the subject is exposed to dark magic while in the womb, Negative Life Syndrome leaves the subject’s life energies tainted by undeath without making them truly undead. common symptoms include intolerance of radiant magic, aversion to sunlight, and the inability to set foot on hallowed ground; rare symptoms include healing from negative energies, sudden necrosis, and the desire to eat flesh or drink blood of living beings.
lycanthropy
Early Life Possessions: the subject was possessed by a spirit or demon during early childhood or infancy, and the possessing presence was in control of them when they learned important milestones, such as how to walk or speak. The subject is now dependant upon the possessing presence to help them perform these tasks or, in cases where the presence has since been exorcised, performs the relevant tasks at a level appropriate for an infant or small child.
Body requires nutrients not found in human food, and you must eat rocks, or gems, or some other alternative. You may or may not have the ability to actually digest these without magical assistance
Awareness of too many dimensions makes it difficult to interact with just this one - either to keep track of conversations, or walk to specific locations without ending up on another planet instead
Telekinetic psychosis - delusions tend to physically affect those around you (but HIGH chance for ableism in this one!)
you have flare-ups where your skin tends to slough off and be replaced by some other substance
After sharing life energy with a dying loved one, you’re now both trying to survive off one person’s supply. Like chronic fatigue, but if your loved one gets too big of a bruise you won’t have the energy to get up until it heals
living in reverse
stuck at a certain age
supersenses lead to constant overstimulation
you’re a changeling, and if you don’t have someone who loves you close by, you’ll turn back into sticks and mud
One that I like is the idea that paladins (and anybody else with supernatural immunity to disease) have their own “disease” in the form of severe allergies. If you’re magically insulated from ever catching any disease, ever, your immune system isn’t getting any kind of natural use. So it overreacts to everything. Being immune to being sick makes them “sick.”
Mages that have complications of their own magic, such as Pyromancers overheating if they don’t let off a fireball now and then, or conversely, being prone to hypothermia and needing their fire magic in order to stay warm.
Telepaths who can’t switch it off and are constantly bombarded by the thoughts and feelings of the people around them, forcing them to wear iron helmets just to get around in public spaces without sensory overload.
Your immune system has got wrapped up in your magic (a common complication in families with multiple generations of powerful mages). Now your fevers can set your sickroom on fire and illnesses that would cause fatigue in most people will send you into an enchanted sleep.
The human body has a lot of salt and iron in it. In rare cases, this can cause half elves to literally be allergic to their own bodily fluids. Not normally fatal (as fatal cases don’t typically survive the womb) but very uncomfortable to experience.
You were cursed/blessed with some dramatic change to your body by a magical entity who didn’t know/care how your body actually works. No you can’t just slap wings on a human and expect everything to connect properly with zero complications.
Most humans with a trace of merfolk somewhere in their bloodline suffer no major effects barring a tendency to be good at swimming and a psychological draw to the sea. Every few generations, however, you get a person who has to keep their skin constantly wet so as to avoid drying out.
