Hello and thank you for using JustAnswer health.
Most likely you will first have an IV. You may be familiar with this - a very small needle is placed into a vein. This way if you are extremely nervous, anti-anxiety medication can be given to you before the needle is inserted in your spine to give you a nerve block. The skin on the spine will first be numbed. Then you will not feel the needle as injects the numbing medication to the nerve root, which will cause you to be unable to feel any pain in the area of your shoulder.
Then indeed, you will be able to take a dose of the oral pain medication before the nerve block wears off.
The doctor will use x-ray to see where to inject the needle into your neck. There is only a very slight chance that he will have to take it out and put another back in, but he is required to warn you about that, just in the rare case that it occurs.
Side effects very rarely could include dizziness or headache after the procedure.
It is important for you to think positively about the procedure and to visualize it going well. Studies have shown that people who are highly anxious before a procedure are more likely to have negative outcomes (side -effects) than those that are able to control their anxiety before hand. So this means it is important for you to take slow deep breaths and be clear in your mind that this is a positive procedure that is going to help you.
Please reply to this post if you have questions so that we can assist you until you are satisfied with your answer.
They can still provide you more medication if needed at the time of the procedure if you are too worried. You need to take control of your worry and do techniques to stop your worry.
Study this: "How to stop worry":
The doctors know what they are doing and will not do anything that is of greater risk to hurt you than to harm you.