I hope it all goes ok! Just try to breath and take it slow. You can also take breaks when you nee3d to.

The other thing I would suggest - if possible maybe write down the main points before you go so you don't forget them? Also, can you talk to the mediator before walking into the mediation session and explain that you are stressed about this and why? Most mediators I have met over the years are very open to discussion about how they can support you to communicate effectively with the other party.

Good luck