OK, first of all, leaves+bridge+wet=disaster. Period. yikes! Glad you're OK.

I'm not by any means an expert, but I've been more of a mtn biker than a road biker. I ride a middle of the road hardtail, a Kona Cinder Cone and have had my share of falls, including a broken bone. For the downhills, one of the things that is helpful, and you've probably already read this, but I'll say it anyway, is to look further ahead down the trail. Don't look at the next move your bike needs to make, but at least 2-3 moves or further ahead depending on the terrain. Your bike and brain really are connected and you'll get thru the downhill stuff better if you're not looking at the root you're going over. If you're looking at the root you're going over, you can't anticipate the next move you need to make. If a rider does that, they are in crisis management mode all the time [Oh sh%*, a rock. (goes over rock.) Oh sh#$, a root (goes over root)] instead of enjoying the flow of the ride (root, rock, root, trench, straightaway flying downhill). Switchbacks are tough anyway you plan it, but if I know I'm headed for a long tough descent (usually the case if there are switchbacks), I'll lower my seat another 1-2 cm (or more even sometimes depending on the grade), a total sacrilege for road biking, but a must for lowering my center of gravity for a big bumpy downhill. The lower, the more stable for descending. In the really steep stuff, my tushy is hanging totally off the back of my saddle, making NO contact whatsoever with the saddle. This shifts weight to the back wheel and helps prevent the a$$ over tea kettle scenario. Practice on some mod-steep stuff to get the feel. If you can't get your hiney off the end of your seat easily, your seat is too high. Mtn biking is soo different from road.

Anyway, it is a learning curve, but it's SOO FUN! I do love it, even when I still eat sh@#..... HTH.