It happend to me twice,
I was searching for bus wheels. I found them in a little shed with an edge at the entrace where you can step over. I picked up the wheels, I exited the building and just tripped over the edge of the shed, fell on the ground and just died right after. Another time I was walking on the top floor of a police station, walked down the stairs and just tripped and died again.
It's really de-motivating when this stupid thing happens and really doesn't make me want to play the game, because I just lose all my progress in a matter of seconds.