It's amazing how stupid people can be when oxygen deprived. My dad had decompression chamber training with the Aussie air force. They gave everyone a clipboard questionnaire with some simple puzzles. In oxygen-deprived state most people were writing off the edge of the clipboard and on their legs.
True, but it doesn't really fit with disabling the transponders and changing course moments after communicating normally with ATC.
Any theory other than deliberate action seems to rely on several major coincidences. Not strictly impossible, but definitely not the most plausible option.
