1) everyone in Helovia loses their memories, those memories are replaced with someone else's memories.
Aka
Apollo loses his memories and temporarily inherits Ktulu's memories.
Ktulu's memories are lost and replaced by Cashmere's memories.
Ect, ect. The solution could be a number of different things. Such as everyone questing the person who has their memories and doing a swap.
2) NOTE: we could also do a body swap; memories stay intact and the mind simply switches bodies.
Sleeping plauge ::
A plauge that slowly starts putting people to sleep, eventually leading to death. Much like a virus.
I'll add to this later....