[ More nodding on his end. ] Just taking things like placebo drugs or psychosomatic illnesses into account, it's easy to see how our brains could be tricked in such a way that it has a physical effect.
Not to mention psychotic breaks or episodes that can be perceived as so real that the person experiencing them can't even tell what's happening until after it's over... if even that — there's a condition called Capgras syndrome where the individual suffering from it is convinced that everyone they know has been replaced by identical impostors. Their brain won't allow them to recognize their loved ones for who they are anymore.
These things are generally treated by anti-psychotic medicine and therapy so... maybe by combining these two scenarios, we'll be able to find a way to break it?