You were on a very strong drug for more than the manufacturers recommended length of time, they suggest only 2-4 weeks but I've seen dependence happen in as little as 10 days. Stopping cold turkey is dangerous and can lead to severe withdrawal symptoms, I know this because I quit that way too. All of your symptoms are caused by the cessation of the Xanax, but I'm not convinced the sciatica is.
Recovery is possible but it takes a long time, when your brain sensed the presence of the drug it made changes to accommodate it and now that the drug is gone, your brain has to reverse those changes and this takes time.
Adding more medications while going through this can be tricky, your central nervous system is highly sensitized right now so you may not react to these drugs like you normally would, many find the best medicine is time, not more drugs for an already overwhelmed brain.
I'm glad you quit alcohol, it works on the same GABBA receptors in your brain the benzo does so it's a good idea to avoid it until you recover.
The best thing you can do is educate yourself about what has happened and try to distract from the pain and discomfort as much as you can, I'm talking about your benzo symptoms not the sciatica. For that I recommend stretching, massage and most likely a visit to your doctor for a proper diagnosis and possible treatment with anti-inflammatories.
I agree with you, this was the worst experience of my life.