Poor dog. Sounds like he has been through a lot in his life. How old is he? What breed?
Some dog schools have classes specifically for shy/scared dogs and dealing with their issues. If you can locate something like that, I would think it could be the most benificial (or private training). A petco class might be too overstimulating for a dog that freezes--at least for now. Right now it sounds like the task at hand is working through his many issues, not SD training. Taking it slow and not overwheling or flooding the dog with too many things and experiences is going to be the best bet. If you find a training center ask to sit in a class before you take him. Look for something low key--small classes, not a lot going on around the room, a gentle hand by the instructor.
Having a pet can have a HUGE emotional (positive) impact on you, service dog or not. Your experiences with him can also give you the basics for training. Work on training tricks at home. Have you ever done clicker work? It is FUN. Honestly, I think it might be best to ellivaite the stress and make the decision now that this dog isn't going to fit for public access work. However, that doesn't mean he can't be a great at-home dog.
As for your issues, have you explored other ways to get your needs met besides a service dog? Have your tried alarms and other gadgets to remind you to take your meds? Are you working with a therapist to deal with the triggers, coping and response to your panic? Typically a SD isn't a cure all. You also have to be able to maintain some sort of stability, consistancy, and awareness to train the SD for the 18 months to 2 years that it takes before they are useful. My SD is very helpful to me, but I also work very hard with my therapist to deal with issues and have other auxilliary supports in place.
ANyway, welcome. I am glad you have found us here and I hope you find the resources you need.