First and foremost, what you can do is be aware of it, look upon it and accept it. It is completely normal to react with fear and defensiveness when confronted with something new and a little frightening; it is also a part of our evolutionary inheritance. If you recognize fear and accept it in a good Buddhist manner, you are mitigating the strength of it and are on the best path to letting it go. Trust in the intelligence of the plant which wants to heal you, and in the competence of our carers, in whose charge you will be safe and protected. We compare the feeling before an Ayahuasca ceremony with an artist's stage fright before the show: it is not particularly comfortable, but it is also a sign of positive tension and respect for what's going to happen on stage. As soon as you let the ceremony envelop you, the stage fright will lift and you will be transported by the plant and its healing process.