Shadow Sickness is a mental disease caused by either intense exposure to Shadowfell energies, or prolonged exposure to less intense energies.
About
Shadow Sickness that is inflicted by a powerful shadow creature also allows that creature to dominate and charm the target, taking control of their destroyed will. However, this side-effect of charm CAN be over-ridden by using other charming effects and powers, though it does not restore the creature to full health, just simply gives the "puppet strings" to another wielder.
Notable Outbreaks
The Umbral Flood
Tens (if not hundreds) of thousands of residents of Isonhound became inflicted with various levels of shadow sickness when the whole continent was plunged into the Shadowfell, creating Umbralhound.
Cure
Moon energies are known to cure Shadow Sickness, which can include potions brewed with Moonflowers, or help from a Moon Dragon or the Crystal Moonwell, an artifact of the moon clerics known as the Lunarans.
