That happened to me on Mt Hamilton once... Right near the top when it was snowing. I hit a thin sheet of ice and my car just started sliding at about 5mph or even less... I was heading off a cliff so I was about to bail out, had my seatbelt off and everything and had the door partially opened when the car hit a tiny patch of traction (no ice in the patch) which was enough to send the car into a different position and away from the cliff.

I seriously thought I was going to die if I didn't jump out of the car, lucky I got traction when I did because it was a 500 foot sheer cliff!!!