I too have fallen over multiple times even though I have been riding clipless since 2004. sometimes, the ageing brain says one thing and the body cheerfully does something else. I usually pick the most public place to fall over, a stop light, a parking lot at the start of a group ride and even at the end of a ride. Fortunately I haven't taken anyone out in the process but. I had the advantage of having a bike shop that insisted that I spend three hours practicing in the shop with my bike in a trainer and my feet clipping and unclipping at all speeds and gears. In spite of this I still stumbel occasionally. Hang in there and keep practicing. It will come easier.

marni