Dick and his sick son, and the voices Dick hears in his head advising him to go back to the doctor again to inquire about a different illness, very rare, very serious, which Dick does, and the doctors realize their mistake and they perform emergency surgery and save the boy’s life.

Wikipedia cites The Science Channel for this story, but I found a better reference:

Pulling the Cosmic Trigger: The Contact Experiences of Philip K Dick & Robert Anton Wilson

It rambles after the PKD section, for better or worse.