This happened at an IBM headquarters location, I didn't work there but I knew people who did. There was a gentleman who was near retirement and was known to fall asleep at his desk in the afternoons. So it was common to see him asleep at his desk. One evening security got a call that he never made it home that day. Security went to his desk and found him, he had passed away in his sleep. Those who saw him at his desk that day had no idea what happened.