Faulty magic

Faulty magic is a condition known among the mages of Mirateia and is considered rather unlucky to acquire.
The way a mage can acquire the condition is if they are unlucky enough to have handled magic ingredients such as mushrooms where the mages can pick up an infection that if not discovered within the first few days will result in the magic of the mage beginning to become faulty and spells will require twice the amount of energy to cast for it to even have a chance to manifest.

Transmission & Vectors

The infection is typically transferred through the touch of contaminated ingredients used in magic.
The infection will after a period of up to 5 days begin to affect the magic of the infected causing faults in their magic to appear.

Symptoms

It can be hard to distinguish the condition from other more common infections until it reaches the state where it begins to affect the magic. 
A skilled doctor will be able to spot symptoms like a dilated left or right pupil and the infected will also be more tired than normal due to the increased energy needed for casting spells.

Treatment

Normally a week or two in bed will be enough to cure most cases of the infection, but if the infected have access to another mage, either in form of a doctor or some of the clerics in the temples, the infected can seek treatment there and get the treatment period down to just a couple of days.

Affected Groups

Mages and other magic users, some versions have been observed to have infected animals, which has led scholars to believe that the infection started in animals and later on spread to mages.

Prevention

Certain amulets work but they tend to be rare due to the infection being somewhat of a rare occurrence and the relatively low number of mages compared to the regular population.

Cultural Reception

Non-mages who have a friend that is a mage, will if good friends, joke

Type

Fungal

Origin

Natural

Cycle

Short-term

Rarity

Rare