PKD remained surprisingly lucid and self aware of the likelihood of suffering from some sort of mental illness. He went back and forth the rest of his life trying to figure out whether he was insane or whether he'd had "real" spiritual experiences. But as the characters in his books learn, there may not even be a clear distinction between the two.

From VALIS (which was largely based on his experiences):

> What he did not know then is that it is sometimes an appropriate response to reality to go insane.

> Let it be said that one of the first symptoms of psychosis is that the person feels perhaps he is becoming psychotic. It is another Chinese finger trap. You cannot think about it without becoming part of it. By thinking about madness, Horselover Fat slipped by degrees into madness.

> People suffering nervous breakdowns often do a lot of research, to find explanations for what they are undergoing. The research, of course, fails.

> What struck me was the oddity of a lunatic discounting his hallucinations in this sophisticated manner; Fat had intellectually dealt himself out of the game of madness while still enjoying its sights and sounds.