ANSWER - I can give you an interpretation but you haven't given me all that much to go on here. It would have been helpful to know who told you that you have been sent as a volunteer and in what context you were told this. There is also a touch of confusion in the sentence "I was sent as a volunteer..." The nature of a volunteer is one who does something voluntarily. You cannot be extorted to volunteer, you do it from free will.
With the above in mind the "sent" in your question changes its meaning in my view from sent as in told to volunteer to sent as in sent from one place to another. So my interpretation would be that you have lived before but have chosen to come back to the earth for another lifetime. The fact that you were referred to as a volunteer would suggest that your reason for coming back was not for personal gain but to offer something (knowledge? experience?) to somebody else. This could be a specific person or it could simply be that whatever you have to offer will benefit others in general. We don't know enough to determine that for certain. However I would guess that the fact you have become a healer in this lifetime would be a fairly strong suggestion that you have come back to undertake the role of helping others and that you have chosen healing to be the way that you do this.
It sounds from what you say that this lifetime was very much your choice and as a psychic and healer you are in a good position to know if what you are doing is having a genuine benefit to others. If so it would appear that your decision to volunteer for another go on the mortal coil was a wise one.