I had a similar thing happen to me around 20 years ago, just the Pilot and me on a Kingair operating a charter flight from Brisbane to Townsville.
He nodded off to sleep for most of the flight, and I just assumed that was it as he said he was very tired, never considered he could have passed out, which luckily he hadn't and he woke up well before TSV.
Why do they still allow these flights on Kingairs with only one Pilot.