I've been wondering about that, and from basically stalking Reynir, I noticed two things:
1) Upon waking up from a vision in which a ghost burst his head into pieces,
he bumped his head against Emil's bunk.
2) Remember that
this happend after he got an angry beating from Onni in the dreamworld.
Of course, I may be reading too much into things. Only time will tell if there actually is anything to it.
My current headcanon about how injury transfer from dream world to real world works is pretty much lifted from what I remember of the time travel in the first
Futurama movie. In there, if two versions of the same person end up in the same time, the one that shouldn't be there is doomed to die within a relatively short span of time, from sheer bad luck. However, one of the twists of the movie relies on one time-duplicate managing to dodge that particular bullet for months.
In that logic, Onni just happening to have young children trying to cut his hair right when he had contracted an IOU for a hurt ear made the perfect setup for fate to collect payment immediately. I personally wrote a fanfic that assumes that Reynir actually hits his head on Emil's bunk on a regular basis because of the sleeping arrangements, so I consider the dream ghost attack was easy to redeem as well. But if the person's circumstances make receiving the right injury in the real world too unlikely, it may take longer to happen.
