Magical psychosis
Magical psychosis is a quite hazardous syndrome that can affect spellcasters doing nothing more than visiting the Astral Plane. This disorder seems to affect wizards more often than priests, though the exact reason for this is as of yet unknown.
On any visit to the Astral, a wizard has a 1% chance of falling victim to magical psychosis, with a priest having a 1% chance every other visit. If this disorder does manifest itself, the victim has a single Will save vs. DC 10 to avoid the effects. If this fails, however, the victim has succumbed to the psychosis, becoming homicidal, schizophrenic, and paranoid.
If it manifests, this disorder can be cured only through magical means of restoring ones sanity, such as a restoration spell or psychic surgery.