OOC Discussion II
Just a little clarification on that point, since I know you're new to the Dragon Age milieu.
When mortals dream*, they are connected to the Fade, where spirits reside. For most folk, this is a fleeting connection that usually results in impressions being left in the Fade, and also in their own memories. For mages, however, because they have a stronger connection to the Fade through their manipulation of arcane energy, this is a deeper interaction that can lead to getting lost in the Fade (and never waking up in the real world) or being possessed by a demon (being turned into an abomination).
These, of course, may not be things Fost understands. What he does understand is that demons do cross over from the Fade (and cause all sorts of havoc) and they can possess mortals.
* Dwarves don't dream, and can't make a connection to the Fade. (As such, they can't be mages.)