Brainburn
(Also referred to as toxic agonotraxis.) A traumatic disorder suffered by wizards who have become involved in too powerful a wizardry without appropriate safeguards, or in cases where the spell's power output overflows safeguards already in place.
The human nervous system has only a finite ability to manage the additional energy "throughput" of a spell: a significant part of the structure of even small spells is devoted to insulating the body from the energy contained or invoked into the spell proper. When the insulation fails and the energy involved is too much for the body to deal with, brainburn ensues.
Brainburn's effects are mostly neurological, manifesting themselves in symptoms like loss of consciousness, memory loss (either temporary or chronic), and/or ataxic or paresthetic symptoms (tremors, loss of balance, tingling or burning sensations, or partial paralysis, usually temporary). Depending on the power of the spell and how much support the "burned" wizard receives after the accident, recovery is usually complete, though it may take some time. Conventional medical assistance may also be required to deal with the strictly physical aspects of the symptoms.
<spoiler>In WAW, Tuyet and Nguyet both suffer from brainburn on the Moon, though Nguyet's case of it seems more severe than her brother's.</spoiler>