This can be a real issue. Everyone reacts differently to being in a dispute. Obviously some people will become angry and emotional. They may become aggressive.
If you have concerns about how reactive the other side may be then you must raise these with the mediator before the mediation begins. It may be that you can arrange good ground rules about how everyone will behave and these may be enough.
Or you may need to have other people present to give you a sense of security. Potentially the entire mediation can take place in different rooms with the mediator walking back and forth between the rooms.
One new method of mediation is to do the mediation by telephone. Usually this is because the parties are not in the same place, however, it could also be used if you had safety concerns.
There are lots of ways in which the mediator can help to make the mediation safe and secure for everyone. If you are worried speak up.