With mental illness this is reversed. One has to prove beyond all reasonable doubt that the person is mentally ill. Gary Heidnik had 25 hospitalizations and 17 suicide attempts prior to committing the crimes he did, and he did many strange and bizarre things over the course of the four months he held the women captive. And then they were allowed to present, unchallenged, the argument that he had an IQ of 147 and therefore he could not be insane. According to this understanding, virtually any combination of realities can coexist.
Extraordinary capability can exist side by side with delusional reality.
The shift to the infant mind can be very incomplete. If he could drive a car or invest in the stock market, he must have known what he was doing. When the infant is in charge, it can utilize some of the automatic functions of the adult. This question indicates a more sophisticated level of understanding.