This anxiety/fear thing when descending sure takes the fun out of riding. I went through this during the summer. Not sure why but I think a couple very windy days contributed. I was almost knocked off the bike by strong gusts and I got scared. This somehow transferred to being afraid I would fall when descending at 30mph or so. I have typically been fearless when going downhill and love the rush and the feeling of total abandon.
Out of the blue, I found myself dreading downhills and started using the brake every few seconds.
I checked my position on the bike and realized I was doing some things that made the problem worse. I was grabbing the handlebars so tightly that it caused the front wheel to shake. I was imagining crashing instead of enjoying my ride. My entire body was tense. I was looking down instead of looking ahead.
I made my arms and hands relax. I reminded myself that I have ridden downhill with confidence in the past. I got my body to move with the bike. I discovered that bouncing gently distracts me from locking up. I raised my head up to get my eyes off the pavement beneath me.
I still have occasional problems, but I don't beat myself up.
The moment of fear is so convincingly real that everything seems to close in. But, much of this is the mind's interpretation. Ride down a short hill and practice mastering the skills. Good luck!
Barb