As you would expect from any professional, safety is of paramount importance, both yours and mine.
The very act of visting a Mistress causes anxiety and stress in varying degrees - that is part of the appeal for many of my visitors - and not surprisingly some of the activities that take place during a session can add to that.
So your first act of safety is to be sure that your general state of health is adequate. This is only something that you can judge, but one possible action you could take is to consider visiting your GP and saying that you are about to start an exercise regime (well - you could call it that!) and ask whether you are fit enough for that. In many ways the two are similar and if you are fit enough for one you are likely to be fit enough for the other.
If there is anything I need to know before we go into a session please ensure you inform me, so that I can act accordingly should anything happen.
Not surprisingly my safety is important too! Letting strangers into my apartment can be risky even though most of my visitors are very respectful and offer no risk at all. However I do have to allow for the possibility of something going wrong or a visitor turning nasty, and I have very effective mechanisms in place for dealing with such situations. Again, not surprisingly, I am not going to publish the details of these!
As with many pastimes, sports and activities, some are more risky than others and you should know what the risks are associated with your particular preference. For example, edge play and other extreme activities are more likely to trigger an unexpected reaction.
To find more about safety in BDSM and your particular activity, search the web as there is lots of good material out there. A good place to start is Informed Consent, and in particular, Informed Consent Encyclopervia : Safe