Mediators do not make decisions. A mediator can only try to get the parties to settle among themselves. So, if there was a decision made during mediation, then it was made by agreement between you and the employer or workers comp insurer.
You may be thinking, "I didn't agree to anything," and you may be correct. However, Georgia law permits your attorney to agree to a settlement without your express consent, and you are bound by your attorney's acceptance, unless you instructed the attorney in advance and in writing that the attorney had no authority to settle.
At this point, I'm betting that the "clouds are starting to clear," and you are suddenly realizing that you have been bound to something that you would have never agreed to, had you known in advance that your attorney could settle the matter whether or not you agreed.
It's notable that in many state jurisdictions, an attorney who settles without his/her client's express consent, can be disbarred for a breach of loyalty to the client -- and the settlement agreement
would be void. Unfortunately, Georgia is not one of those jurisdictions.
Your recourse would be to refuse to cash the check and then claim to the workers comp board that you did not agree to the settlement and that your attorney was instructed that he/she was not authorized to settle without your consent. Whether or not the WC board would accept this argument is uncertain -- the biggest problem will be that your attorney may decide to "throw you under the bus" and claim that you never removed his/her authority to settle (because, otherwise, the attorney would be open to a malpractice suit by you, and the State Bar of Georgia could discipline the attorney for that notorious breach of loyalty that I've already described).
That's how your question plays out. Unfortunately, you may be stuck at this point -- but, before you decide to start a war with your lawyer, I would encourage you to sit down with him/her and try to explain the situation -- because, maybe he/she will have an idea that I haven't considered, given that he/she knows more about your case than I ever will.
Hope this helps.