Mine happened when I was skiing. Last person on the lifts before wind closed them - high level, above the tree line. The wind blew me along to a faster than running pace. But the first I knew of it was when I could feel I was moving, rather than see anything. I inevitably crashed. When I could eventually see, my brother had crashed right next to me - literally a foot or so away. I was lucky in that I was then on a sheltered part of the mountain and could get down, as the wind had dropped. Another way of describing it is like when you first go into a dark room or a deep cave, where everything is black. It's just the reverse and everything is uniform white. I pity anyone who gets caught in this situation for any length of time.