[NoPie]

Diazepam can sometimes cause people to act like that. They are not sleeping but are completely on autopilot, even driving a car etc. and afterwards they don't remember what they were doing.

Some people are afraid to fly and use diazepam to reduce anxiety.

It might not be what happened here but this would be my first assumption. He somehow got on the wrong flight and lost his memory due to use of drugs or stress.