Read it through once

I should have gone to my grave puzzling over that riddle but for that lady’s chance question last week: ‘Have you ever had a vision—when awake?’ It stands explained now. During at least sixty seconds that day I was asleep, or at least totally unconscious, without suspecting it. In that interval the man came to my immediate vicinity, rang, stood there and waited, then entered and closed the door, and I did not see him and did not hear the door slam.