Are some forms of “mental illness” or madness, in fact, a form of involuntary and uncontrolled “seership?” What can Creator tell us?

You are hovering around an important truth here in your question, that somehow the plight of the mentally ill has some connection in seeing things others cannot. The reality is that mental illness is not a product, alone, of seeing or over-seeing, in having too much awareness for one's good. Mental illness is a consequence of inner corruption, typically by dark spirit possession. It can have karmic roots as well and often the two conspire to make a perfect storm of inner liabilities. When someone who has vulnerability to being manipulated in a deep level of their mind also has the capabilities of a seer, they will be much more likely to hear the voice of such dark spirits brought to conscious level through their intuitive reach. In a sense, they are channeling their inner demons and can talk to them. This is a highly dangerous state of affairs because the spirits will have a field day with the mind of their host, tormenting them relentlessly to mock and terrorize them by turns and, with conscious awareness of this harassment, the damage will be much more severe because then no level of the mind is spared from the attacks, and this will greatly undermine a person and even incapacitate them, ultimately. The origin of delusional thinking is a programming by dark spirits within, to create a kind of looping of thoughts that do not serve the host, that are a kind of lie they have been made to believe and to think it is important to focus on, and a part of their mind will take up that task and replay those thoughts over and over and over again. Delusional thinking is not only a distraction but heavily destructive and often creates a downward spiral through a worsening. People can only take so much, and this may end in suicide or acting out their inner dark thoughts to harm others, feeling compelled to do so, because it is what their own mind, seemingly, is telling them, when in fact it is a demonic being taking charge of them. So, in such individuals, being a seer is a liability because they will be unable to avoid becoming preoccupied, with their own world being turned upside down by interlopers wanting to harm them, and will see and feel and know quite painfully the reign of terror being inflicted without understanding its true origin, meaning, and purpose.