Manatoxicosis

Co-written with OranTheWise
Manatoxicosis is a condition caused by repeated overuse of Mana that can lead to death.

When a patient has ran out of Mana but keeps casting spells, and before the body has the ability to regenerate Mana, the body starts to break itself down to produce the components necessary for spellcasting. This phenomenon starts with a dilatation of veins and arteries, accelerated heartbeat, light-headedness and a feeling of weakness. If the patient does not stop at the first signs, it's followed by a fainting episode.
  After regaining consciousness, the patient feels drained and out of breath. Occasionally, heart pains are also reported, although more often seen in patients with lower Mana levels. The veins of the subject stay dilated even after regaining consciousness, usually making them visible in areas like the foreahead, hands, feet, and neck.
  From this point on, the subject must excercise caution when using Mana as their threshold is reduced. If Mana is used before a full recovery, the same symptoms occur, but much faster and at a greater intensity. Twitching may begin during the fainting. The condition isn't fatal at this point yet, but the risks increase greatly. The patient, upon waking up, typically starts suffering from recurrent headaches and notices a diminution of some or multiple of their senses.
  The frequency and intensity of the episodes increases if no measures are taken. Furthermore, the repeated dilatation of the veins weakens the walls, leading to a heightened likelyhood of rupture and subsequent internal blood loss. The subject generally also starts reporting sever heart pains, described as having their heart squeezed tightly. Depending on the severity of the symptoms, Mana use might be totally forbidden.
  Recovery includes a strict period of rest, treatement to heal internal damage and sometimes pilmigrages. With the agreement of the treating doctor, one may start casting spells again, although caution is advised and patients are encouraged to stop at the first signs of exhaustion. Some signs remain after a full recovery, such as an increased risk of syncope, heart problems, headaches, and more commonly, swollen veins.
Cause
Overuse of Mana
Symptoms
Dilatation of veins and arteries, hypertension, light-headedness, weakness, feeling drained, being out-of-breath, heart pains, seizure, headaches, diminution of one or multiple senses
Complications
Fainting episodes, seizures, complete or partial loss of one or multiple senses, blood vessel rupture, internal blood loss, death
Treatement
Strict rest, healing of internal injuries, prohibition of Mana usage, pilmigrages
After-effect
Increased risk of syncope, heart problems, headaches, swollen veins, diminution or complete loss of one or multiple senses, permanent diminution of Mana levels
Type
Physiological
Rarity
Common
Affected Species
In-game effects
Character loses the amount of HP corresponding to the amount of MP required for given spell, lost HP cannot be recovered by healing spells and only through Rest