Hi Mary,
I have had multiple Lumber sympathetic blocks, some have worked well for quite a while and some have been quite short lived but I am always happy to have another go.
They will lie you face down and hopefully give you some light sedation so that you will actually sleep through the procedure.
I have had one without sedation and I found it just too hard to keep still as it was painful just lying that way.
They should use fluroscopy/image intensifier to find the sympathetic nerve so as to maximise the relief.
When you wake you will probably feel a very warm sensation in your leg. It will probably look quite pink too, this is a sign that the anaesthetic has hit the right spot.You will often have a numb pubic area and parts of your upper leg maybe numb to touch. Walking is usually not affected unless you have had a very generous block that has hit the motor nerves also.
There is some discomfort on your back where they insert the needle and sometimes a bruise but compared to the pain we aare used to it is usually quite easy to manage.
Sometimes the pain relief is not immediate, don't despair if you feel no change, it can take a day or so before it kicks in.
I wish you all the best with your block, look forward to hearing how you go.
Cheers Tayla:

addit--My Pain doctor injects lignocaine into the block, he once included some steroid but only the once