It's a common theme is 'parallel universe' stories. I've long considered a 'mental health issues are actually demons from another dimension plaguing sensitive individuals in this one', but haven't acted on it yet (it's in the planning stages at the moment).
The tricky part, as with any parallel universe story, is in making alternate universes believable. Not only do you have to argue for duplicate universes which are symmetrical in all aspects but one, but then you've got to propose some method of communication between the reality of one and the dreams of someone in another (it seems overly specific, without a justification for why that one individual out the the entire universe was selected).
But then, sometimes fiction is just fantasy, consisting purely of magic rather than logic.