There are a lot of all natural calming pills or liquid drops on the market. Some work some don't, it is hard to say.
What exactly is wrong? What does your dog do, and how do you leave him? If you are nervous, sweet talking, or babying him when you drop him off, all that does is make him worse. Your dog, esp. companion breeds feed off of your emotions no matter what you say. So if you are nervous, he is nervous. Be matter of fact, and don't worry. If it bothers you that much, then consider a different groomer. Wait for him instead of leaving him. If he is really nervous, it would not be a good idea to watch, it would only make him worse.
Let me know what he is doing, and what his problems are maybe I can help. I have been grooming for a long time, and I think I have seen most of it lol.
Have you tried desensitization training? I advise my Poodle puppy buyers to brush & comb their puppies EVERY DAY, as well as handling their feet, faces, tails, etc. do you do any of this at home in order to get him accustomed to it? If you answer some of the above poster's questions we could offer better advice more specific to your situation.