In the scene at the airfield, Indy attacks and knocks out a German mechanic wearing a cap. Watch carefully as he punches the guy in the face; he hits his head on the side of the plane and lands on his back (well, partially on his side, to be pedantic) in the dirt, out cold. Later, when the petrol flowing around him rouses him back to consciousness, we see the knocked-out mechanic clearly lying face-down as he wakes up.

Must have been doing some sleepwalking.