Should health insurance underwrite past-life regression therapy?

NO

Absolutely not. If you’re miserable in this life, it’s not going to do you any good to know that you were miserable in a prior life, too.
Happiness is a concious decision, that you make. It can ONLY come from within – in THIS lifetime. Strive to be content – it’s pretty much the same thing.

Not positive I understand your question, but I gather you are asking if a health insurer can underwrite (investigate and measure risk) for treatment you received. I believe you are stating you received hypnosis to analyze what may be going on today based on something/many things you believe may have happened in what you believe was a past-life or lives.
If that is what you’re asking, I’ll answer to that. I was a former life/health underwriter before I became an agent and yes, underwriters will measure the risk of claims as they relate to the symptoms and treatments you are receiving in today’s life.
Basically, they’ll want to know why are reveiving this treatment? Are you depressed? Suicidal? Just curious? Are you on RX for any of these symptoms, if so, what kind and how often? They’ll be trying to get to the bottom of a diagnosis.
The underwriter in me suggests that you’re seeking answers to a problem you’re experiencing today. What’s the problem and how much of a risk does it pose to your mortality and morbidity?