Apocalyptic Despair Syndrome or Asymptomatic Demise Syndrome (henceforth http://zombie.wikia.com/wiki/edit/ADS%20(syndrome)/0abbreviated as ADS) is a form of mass hysteria that took hold of most Safe Zones that created shortly after The Great Panic began to subside. Separate from the mass waves of suicide also occurring, ADS was the name given to the phenomenon of extremely depressed or distressed survivors suddenly dying in their sleep with no pathological or physiological cause of death to be found. It was generally described as people literally succumbing to the feeling that tomorrow wasn't worth living for, when it still looked likely that the Safe Zones would collapse and a complete zombie victory seemed inevitable; after a prolonged period of such stress and depression their minds and bodies just gave out.
Statistics vary from zone to zone, but most zones experienced losses of 4%-10% of their post-barricaded population due to ADS.
A major remedy for ADS was discovered by director Roy Elliot, whose films Victory at Avalon: The Battle of the Five Colleges and Fire of The Gods dramatically lowered ADS rates in populations where it was shown.