Hall of Mirrors by Frederic Brown, Science Fiction, Fantasy, Adventure

For an instant you think it is temporary blindness, this sudden dark that comes in the middle of a bright afternoon.

It must be blindness, you think; could the sun that was tanning you have gone out instantaneously, leaving you in utter blackness?

Then the nerves of your body tell you that you are standing, whereas only a second ago you were sitting comfortably, almost reclining, in a canvas chair. In the patio of a friend's house in Beverly Hills. Talking to Barbara, your fiancee. Looking at Barbara -- Barbara in a swim suit -- her skin golden tan in the brilliant sunshine, beautiful. . . .