It was in 1981 and he had to take a break from working at Apple due to his injuries

So he had an accident while flying a cesna that he shouldn't be flying, and suffered a head injury.

Infinite Loop, the book about Apple stuff, said that "Coming out of the semi-coma had been like flipping a reset switch in Woz's brain. It was as if in his thirty-year old body he had regained the mind he'd had at eighteen before all the computer madness had begun. And when that happened, Woz found he had little interest in engineering or design. Rather, in an odd sort of way, he wanted to start over fresh."