The fact that there is a mandatory mediation, and not a voluntary mediation, scheduled would indicate that there must be some type of petition pending. I am assuming that this is a petition filed by the Insurance Company,and consequently, your benefits may be being placed in jeopardy. If you have not done so, you should discuss this with an attorney immediately. Mediation can be a very useful procedure in getting cases resolved, but it certainly sounds like there are some issues with your case that need to be discussed with someone BEFORE you try and resolve your claim. Do yourself a favor and use AVVO to find someone to discuss this matter with (if you do not already have an attorney).
Both mandatory mediation and voluntary mediation can be very effective ways to resolve your claim, or narrow the issues you are arguing over with the Insurance Company. You should always discuss the pros and cons of attempting to resolve your case via mediation, and also have an experienced workers' compensation attorney represent your interests at the mediation, because the Insurance Company certainly will have representation.