Dreams are strange and powerful things for Oneiro Mance. They are the only reason he knows about Agartha after all. You see, when Oneiro goes to sleep in his reality he wakes up in Agartha and the reverse also true. He's hasn't known anything else since he was five. He doesn't want to.
Unfortunately, the last thing he can remember from his world is a terrible accident. The screams, the fire, the blackness in his vision making the world fade away. He woke up in his Agarthan home, screaming, and has tried to fall asleep ever since. For him, this insomnia is more terrible than the memories of the accident because he doesn't know if he's dead in his world or not. So he's gone to Avalon, hoping he can find a way to fall asleep again, or even just learn what happened over in his reality.
His insomnia has had one beneficial element. He never tires, and has started studying his paper magic more intensely, even managing to master the extreme basics of cardcasting.