If a Moonflower glows too Red for too long (or just one of those), their body temperature rises. When a Moonflower's body temperature gets too high, they faint (or "wilt"). 

  This is based on the concept of real-life flowers wilting from too much heat. Case in point, some Moonflowers can take the heat better than others (this would probably include Maroshi).

  (Excessive prolonged anger might also cause respiratory problems)