Wistalla happens in older elves as their bodies wear out and are less able to channel sorcery. It never happens in shorter lived races because they do not live long enough for the parts of their bodies that channel magic to wear out.
Wistalla is when an older elves sorcery begins to fail. It starts out with headaches and bloody fingertips after casting powerful spells. It then begins to affect lower power levels of magic until the magic itself begins to weaken. In its final stages, blood will seep out of the skin all over the body whenever casting even the smallest of spells, and more powerful spells may just kill the elf outright through strain on the body.
There is no real cure for Wistalla, but it only causes damage if the elf casts sorcery. Average elves will usually just avoid magic, maybe going through therapy to recondition themselves from using small spells for everyday tasks. However, if an elf uses magic for their job, then they may go through learning Wisary, elven for "Magic with Wistalla." Wisary is not a full type of magic, but rather supplementary magic that helps elves with Wistalla still perform enough magic to get through their life long enough. Wisary is the basis of what humans later developed into Wizardry.
If an elf develops Wistalla, then they will never be able to fully use magic again. If one continues to regularly use magic once having developed Wistalla, then they will die with a year or two, as continual use of magic accelerates the disease.
Elves who develop Wistalla are mostly older folks, around 800 years old, but sometimes it happens to younger elves.
To make the chances of developing Wistalla lower, it is encouraged for elves with a history of Wistalla in their family to avoid using excessive magic, especially before fully maturing. However, this is not a one hundred percent successful method.