I have written three books - you can "look inside" them on Amazon - as well as scores of articles. My approach to your book would focus on telling the story as clearly as possible - reading should be enjoyable, not hard work. Here is how I'd rewrite the first two paragraphs of your preface:
"My father screamed in pain at the barbaric treatment. I was only five or so years old, but the memory of his agony stayed with me. I said to myself then “there must be a better way”, and now I am a chiropractor.
It was my curiosity that led me down this path. My father took me everywhere he could and when he suffered from bouts of severe lower back pain I witnessed the treatment he received at the hands of an orthopedist. It included being suspended from the ceiling in some contraption and being twisted. So when I had my first episode of back pain when I was 17 or 18 I resolved to find some alternative to what my father had endured.
I heard about a chiropractor in Switzerland, and even though it meant crossing an international frontier and a cash payment I couldn’t claim on insurance, I was determined to find a better way. What I discovered was a superior treatment and holistic approach to back pain that didn’t cost a fortune."
Please contact me if you're interested in discussing your book further with me. I see a chiropractor on a regular basis, so it's a subject for which I have great sympathy,
Cheers,
Mishka