I had a Lidocaine infusion. I felt no difference from it but had no side effects either. It was an iv infusion and the nurse monitored me for the whole time. I cant recall how long it was. I think though I have read of someone getting a benefit cause we are all different.
Though not what you are talking about but one doctor suggested getting a tunneled epidural catheter and then doing physical therapy and like you I worried when the med stopped working I would be in delayed pain.
Usually ketamine is suggested only by doctors who do it. So if you are interested in that you may want to look up a doctor who deals with RSD and does ketamine.
Good luck and I understand the mental impact these decisions plus the pain have.