Faerie Flu

This strange illness comes from mischievous Fey creatures. Many people have been recorded becoming prone to Faerie Flu after disfiguring forests or groves, and show symptoms of light-headedness, nausea, and vivid dreams. In later stages of the illness, victims display violent fevers, rapid changes to emotions, and vomit rainbows.
The only known cure is apologising to the cause of the illness, or killing it, whatever it comes down to.
Many people have different names for Faerie Flu, such as: Unicorn Bug, Skottlis, Jujubal, Huffer's Virus, and Pixie Hex.