Passengers

For three years, people on Earth have been subject to the will of the "Passengers"—intangible beings who usurp human bodies temporarily and without warning, and do nothing but play and cause havoc. People being "ridden" are ignored by others, and when they are freed, the experience, by social convention, is ignored by all. When the Passenger leaves the host body, the person is left with no memories of his time being ridden.
"Passengers" was nominated for the Hugo Award for Best Short Story 1970, and won the Nebula Award for Best Short Story in 1969.