There are meds and possibly training programs to help reduce your dog's stress levels. If he thinks he is in charge and its all his responsibility he may find some stress relief if you take over the perceived pack leadership.
For meds that might help along with a training program I'd suggest asking your vet for a referral to a veterinary behaviorist for the best combination of solutions.
At home while you work on that you can see if trying the nothing in life is free program will reduce his stress by subtley increasing your leader status. You can read about that here
www.idahohumanesociety.com/caretrain/notfree.html
You might also find increasing his directed exercise so he is more tired, and reducing the protein in his diet will help him relax more. So if you are feeding a high protein food you could try reducing to a lower protein food.
Hope this helps you!
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