Crystal Sickness is a disease in Final Fantasy Crystal Chronicles: Echoes of Time. It is apparently contracted from being exposed to high amounts of Crystal radiation. Symptoms seem to include extreme fatigue and glowing of the body.
The Crystal Sickness seems to be able to affect both the living and the dead, as shown when Eryll fell ill with the disease. There is only one cure for Crystal Sickness, with one of the ingredients being a Buffasaur Horn. After a person is cured from the sickness, they grow stronger, never become sick again, and heal faster than normal people. The sickness is usually contracted at a young age.
Known characters to have contracted the disease include Eryll and the Hero.