First, tell your employer. Preferably in writing. Second, tell your rehabilitation nurse if you have one. Again, preferably in writing. Third, tell you doctor. And tell your doctor that you’ve already told your employer and your rehabilitation nurse without any real success.
And here is why it’s important to put things in writing. You want to be able to show your doctor the notes/emails you’ve written showing how you’ve tried to work things out. This is important: when you are writing an email to your supervisor explaining the problems you are having remember that you want to be able to show your nurse, your doctor, your lawyer, and the Industrial Commission that letter.
There’s nothing to gain in writing a sarcastic note to your boss telling him he’s a bonehead who doesn’t know how to run a company. It may well be true but it’s not going to help your cause any. Instead, write a letter saying how great it is to be back and you love the workplace but you’ve got this one little issue that needs help. When he ignores you because he’s a bonehead who doesn’t know how to run a company at least you’ll have something to show the doctor. And you’ll look good in the process. There really aren’t any clear-cut requirements for what a doctor does. So maintaining some credibility and looking good cannot hurt your chances at all.