Snakey, even the well adjusted dogs I've had have been jittery and found it hard to settle when they've come back from kennels, even though they have a ball when they're there and practically drag me down the drive with excitement when we drop them off.
I do completely understand your reluctance to go for medication, but thought I would mention it anyway. Our boy did improve, he never a 'normal' dog, but he was happy with his own 'managed' small little world and we were happy to do that for him to facilitate a life for him where he felt safe and happy.
I bought an amazing downloadable seminar from Suzanne Clother's website (incredible woman) last week. It was Arousal, Anxiety and Fear. It cost $20 but it was money well spent, as it really helped me to understand these things from the dog's perspective, better than I ever have before and also gave me a great insight into how to handle my current fearful pup (nowhere near as bad as my GSD x boy, just some fear around other dogs that is really improving).
One of the things she said that really struck me is that you simpy cannot counter-condition or adjust the behaviour of a dog that is in a state of high anxiety. She explained the pyramid of dogs' needs with food, water, shelter etc as the largest section at the bottom and the next biggest category being safety.
She went on to explain how we need to do whatever is necessary to get the dog into a position he feels safe in, before we can even begin to think about changing their response to the stimuli. She also said that some dogs will never get there and then it's about management and making sure we give them the best life possible, whilst ensuring that we have done everything in our power to make sure that neither they or anyone else is ever put at risk. It was the first time I've ever heard anyone validate the route we chose to take with our boy, after years of intensive behavioural work and much soul searching. It actually made me cry. 
Do remember what we talked about before as well. Give yourself a break, both you and he need to step away from the stress sometimes and time spent playing with him at home, training and either just having short walks or walks in carefully considered remote places will benefit you both. Neither you or he can live permanently full to the max of anxiety, sometimes you have to take a step back and just BE, it will do you both the power of good.
As nutty said, give him a really quiet week, give him chance to regroup and feel safe again, before you embark on any situations that might push his adrenalin levels up again.
... and be kind to yourself. You are an amazing person for committing to supporting your boy. He is very lucky to have you. 