Drop the seat right down unfashionably low
untill your confidence comes back. The thing you probably fear most is going over the bars, so drop your c. of g. to avoid that.
Do the same run over and over until your body starts to relax and you'll begin to work like one big damper and it feels great.
Run flat pedals for a while, that is a big help when trying to gain confidence.
Look well ahead and keep off the front brake and learn to "go light" its invaluable over rough stuff.
Hit the deck a few times, maybe on mud or soft leaves just slide it out under you, as stated above you're programmed to fear falling off so fall off in a controlled manner to overcome it. The pro downhillers use this technique to find their limits when practicing fast cornering.
I only started to downhill properly once I learned to relax, it is the most importand thing I'd say. I've gone from 8" full sus to fully rigid now and it is much more of a leap of faith hitting a dowhill section you haven't ridden before. Still getting used to my feet being attached to the bike but it's just about practice. Also the body can take a hell of a lot of abuse before it breaks so nine out of ten falls you'll get up laughing.
Lastly , Use the force!! it never fails