@mags314772,
I don't think you should be nervous about it. It's just x-rays done with the use of a contrast dye. The dye travels, and the x-rays will show any blockages of a nerve root or the spinal cord because the dye will reveal these.
My mother had an arteriogram, which is a very similar type of procedure. In her case, the dye was injected to help visualize any blockages in the arteries of her legs, and x-rays then tracked the flow of the dye. As I recall, she had no real problems, or discomfort during the procedure, and I was in the room with her.
The main risks, from tests of this type, that use contrast dyes, are possible reactions to the dye. These risks are actually very small, and many, many different kinds of procedures are done everyday using dyes. If you have any history of allergies to dyes, or simply any history of allergies, you should inform your doctor about them. Even with allergies, they can generally still do the test, they just take additional precautions to prevent an allergic reaction.
I really think you shouldn't worry needlessly. These tests are pretty routinely done, with no ill effects.
I hope the test helps to lead to successful treatment for your back problems.