Donnie Darkos instability

I think his instability is to do with how he can see time because from the scene in the film where he is looking around the living and see's his family members have clear blobs coming out of their torso and direct them. Connoting that he can predict what people can do and where they will go.

Neither. Well, for me at least. I loved it because I thought it was greatly executed and just beautifully done and haunting

Just watched it for the third time a few hours ago and IMO it's a combination of both, sort of like Rain Man or A Beautiful Mind.

There's a dual nature displayed, mental illness juxtaposed to genius,'tuned into' a Higher Power.