Spellrot

"Magic-derived Embodied Field Destabilization", commonly called spellrot, is a class of degenerative magical disease primarily affecting magic users. Frequent spellcasting, regardless of the magical field being called upon, has a chance to lead to a "tangling" of the magical fields inside one's body, which is exarcerbated by further spellcasting. If untreated, the disease causes progressive inability or instability of spellcasting combined with progressive medical issues. Think of spellrot like magical cancer; there's many kinds, it has genetic and environmental components, it's (usually) progressive/degenerative if untreated, and it has some treatments but they're complex and not 100% effective.

Causes

Spellrot is instigated when spellcasting causes particular kinds of magical field entanglement which get "locked in place" and associated with bodily function. For example, a bard using a rhythm instrument to cast a powerful spell, especially while simultaneously blessed by a cleric or concentrating on another spell of their own, runs the risk of forming a "spellrot knot" associated with their heartbeat. There are many kinds of knot for each organ and magic system, but they can generally be categorized by the 1) the field of magic that initiated the knot, and 2) the organ or function associated with the knot. There is not always a clear link between the organ and spell; teleportation knots often embody in the vestibular system, but embody in the spine just as often.
If not caught and treated early, the knot then catalyzes "hooking" other spells into itself, making the knot bigger and more firmly established. This becomes an especially big issue when different magical fields become entangled, as it creates "unstable embodied field harmonic resonance" which causes most of the actual symptoms and physical issues. The whole thing snowballs.

Symptoms

Spellrot has few symptoms in initial stages; experienced mages know what the very slight change in casting "feels" like, but most cannot tell. Educated mages know how to check for early spellrot after powerful or convoluted magic use.
Once the knot is larger and becomes a multi-field tangle, the symptoms begin to appear. The exact symptoms depend upon the organ/function entangled; eye knots could lead to vision problems, heart knots could lead to arrhythmias, brain knots to brain fog or memory issues, etc. However, general symptoms include fatigue, difficulty casting spells OR extreme ease of casting, and instability of spell effects (cast or received) at late stages. As the knot grows and tangles its symptoms worsen, and it increases the chances of developing more knots in other organs.

Treatment

There are many different treatment options, each more appropriate to different knot field compositions and locations. Treatment is always easier on small, new knots, and is quite effective at that stage. Early treatment involves no casting and reducing exposure to magic, resting the embodied organ/function, and a dissipation ritual conducted by a professional, maintaining magic reduction for at least a week afterward. Experienced and well-supported mages have usually done this at least once or twice in their life and made quick full recoveries.
At more complicated stages, intensive professional care is required. Professionals try to diagnose the knot's exact location and field composition, then untangle it in reverse order with ritual tools related to those fields. It's like trying to untanlge a ball of yarn laproscopically inside a tinted glass bottle; possible, but precise and tricky. Auxiliary treatments include alchemical remedies and antimagic fields.
In extreme cases, amputation of the embodied location will completely stop the spellrot, but this is not possible for many organs (the brain, the liver, etc., though the heart strangely IS replaceable with extremely expensive prosthetics or dark rituals).

Prognosis

Early treatment has a very good prognosis of around 96% 5-year survival with proper care. As the condition worsens, the prognosis drops down to between 20% and 2% depending on the specifics. After death, the knot fades and untangles as the organ ceases functioning.

Affected Groups

Some people are more at risk for some spellrot than others. Halflings tend to be quite resistant to spellrot, while Uncommon Races like tieflings are especially susceptible in general. Humans get pretty much every kind of spellrot, while dwarves are extremely resistant to some kinds (tongue, charm, teleportation) but quite vulnerable to others (bone, fire, heart). Elves get spellrot less easily, but it often progresses much faster in them once established.
Within each race, genetics and environment also play a role. Someone who has never had spellrot in their family history is probably pretty resistant, while another could be genetically susceptible to a specific kind.

Prevention

Spellrot can be pretty reliably prevented with proper training. Specific ritual components and methods, extra phrases in spell recitations, and other casting techniques have all been developed to reduce spellrot likelihood, though they all differ between magic fields and styles. Some are bogus, but plenty are actually effective.
Besides technique and experience, reducing spell power/intesity is a good way to reduce spellrot risk. Spells of 1st through 3rd level intensity (to use the Cratic classification system) almost never induce spellrot, but the chance increases from there.
Reducing nearby magical overlap is also good; wearing too many magic items of different magics increases risk of spellrot. The effect is proportional to their strength, though, and some magic items actually have the opposite effect. For example, items with "nondetection" cast on them actually decrease spellrot risk, while Starmetal items increase it dramatically.

History

Spellrot has always existed on Vorago, but was first well described by the Elven Protectorate around 1100 PE. Historians note that a better understanding of spellrot may have been one of the big environmental factors that led to the founding of The Magocratos.
Spellrot rates always go up during any war that uses magic, and was especially high during The Fire Wars and the Brothers' War. Rates spiked even higher during The Destabilization, but have since dropped back to almost pre-Destabilization levels.

Type

Magical

Origin

Magical

Cycle

Chronic, Acquired

Rarity

Uncommon