I had this fear as well. In my personal belief system, and in many other spiritual people's beliefs as well, we choose to incarnate. I don't believe in the "reincarnation trap", that we're forced to re-incarnate again and again against our will. I believe that our soul chooses to return to earth in order to learn lessons, heal karma, or fulfill some kind of specific purpose. The soul isn't afraid to suffer because its main goal is to gain growth and mastery through overcoming adversity and hard times. That's why we may choose to incarnate into painful, difficult, or tragic circumstances because we can glean a lot of insight, growth, and development through the overcoming of obstacles and pain.
I do believe we have the free will as humans to put an end to our lives regardless, though. We may choose to re-incarnate again in order to learn or experience something we didn't experience in the last lifetime, but I don't believe it's a forced occurrence. I believe the soul "maps out" the general trajectory of a person's life on earth, and then we exercise our human free-will to make various choices throughout our lives that serve to help us learn life lessons and experience different outcomes and directions based upon those choices