Were you on all season, summer, or winter/snow tires at the time of the incident?
I hit a patch of black ice coming out of a turn in a residential area yesterday. The back end broke lose but fortunately I was sporting Michelin X-Ice Xi3 studless winter tires on my RWD 335i. I attribute the effortless recovery to the tires. $900 for the tires and installation seemed well worth it in hindsight.