I had an ESI done a few weeks back, I will never do it again and have made this very clear to my pain management doctor. First off the injections are actually pretty bad for you, search around in the pain management board there's a very good description of what it does, particularly over time.
Secondly it was some of the most horrendous pain I've ever had in my life. I do not respond immediately from novacaine like most people so needless to day I basically had it done without anything to numb it. The pain shooting down my legs with the novacaine and the steriod was just not to be believed even though it only lasted about 10 or so minutes then regular pain started in. I could barely walk for 2 days afterwards and was taking vicodin every 3 hours for pain. It actually made my back pain more severe now and the doctor ended up changing my overal pain medication to MS Contin which is stronger since the vicodin now wasn't working at all.
The doctor did not give me nor offer me anything to calm me down, I had a full blown panic attack while he did it and cried for hours afterwards. I warned him before hand if I turned around and hit him it wasn't my fault that I have these attacks. They would not let my husband go into the room with me at all because it was a sterile environment, that didn't help matters any.
If it is going to take you 12 hours to get home I might reconsider. You will probably be ok for the first hour or so but once the novacain wears off you could be in some serious pain. Everyone does react differently. Is your vehicle comfortable? Can you get comfortable in it? If you do go take a really soft pillow so you can hopefully recline if theres any residual pain. Also take any pain medication you may have with you, you might need it.
For what it's worth I've had pretty much all my other primary joints injected over the years and it only worked on my shoulder and it never ever hurt as bad as the ESI does.
I'm not trying to deter you, however, I've only met one person who the injection worked for, and it took him two injections before it actually worked properly. Most people will tell you it isn't effective and not worth the risk overall.
ultimately the decision is yours, and if you do go ahead and do it just be prepared the best you can for your trip home.