I had one of those wrecks too. Grabbed too much back brake, rear wheel slid out and off the side of the trail, and down I went. I was bleeding from knee to elbow on one side and cracked a rib or two on an invisible rock where I landed.

I avoided that particular section of trail for quite awhile...just rode other places. I finally went back to that park and I can't even tell you where I wrecked any more. It was (for me) a process of regaining my confidence overall, and working on enough basic skills that the "surprise" wrecks became a little more controllable. (Less of a panic reflex, which is what caused me to brake so hard to begin with). Obviously I still crashed after that, or I'd be riding today, but even with much more reason to panic now I'm a lot better at knowing what the bike will do in a given situation. It helps mentally settle me.

I use Artista's approach too, and it also helps me to watch someone else ride a section. Especially someone that I know. You can kind of see what to do and what not to do and analyze what you would do differently before giving it a shot.