Actually, i would have thought that the "willing" question would have been the, um, question. That is, you may think you are willing now, but would you freeze up or freak out and no longer be willing to assist in the event of an emergency?

In any case, you could phrase your response as, "I believe I am." It is an affirmative response, but leaves the OP just enough uncertainty as to account for the possibility that he would not willing and/or able should the time come.

As my SAT tutor (my big sis) once told me, don't overthink it.