Several years ago. I too was in an automobile accident. The doctor should explain it to you so you will feel more at ease. But I can share a little of my experience.
I remember being afraid, mostly of the unknown. But I had a really good doctor. He took his time with the procedure. Went very very slowly to make sure I wasn't feeling any pain. He could stop at anytime I began to feel the slightest uneasy and inject more numbing medicine. So I never felt any true pain.
After the first time I was much more relaxed.

I wish you the best and hope it all works out well for you. And especially I hope it eases your pain. I KNOW YOU MUST BE in a lot of pain for them to want to do the injections. But they do it all under xray which is great so they can see exactly where they are injecting the meds.

Good luck!