I want to preface this post by saying that you should, as a health consumer, research the pros and cons of ANY treatment, conventional or not, and make the most informed decisions you can about what to undergo. It's so difficult nowadays for a typical layperson to make these decisions because there's so much conflicting information out there. That's where your friendly medical professionals come in to help. If you're not getting the time and energy you need from your provider, that's when it's time to write a letter, have a chat, etc. or ultimately change providers if all else fails.
Note that I did not say this healthcare provider has to be an M.D. or D.O. There are some brilliant nurse practitioners, naturopaths, etc. who have been infinitely helpful to their patients. The important thing is that you really trust the person and they have evidence or research that they can explain to you to back their methods up.
Here's a link to a consumer-friendly CNN article from 2000: http://archives.cnn.com/2000/HEALTH/alternative/02/08/colonics.wmd/index.html
I am also a big fan of this site, QuackWatch, which has some interesting tidbits about a serious mishap for one woman who underwent a colonic: http://www.quackwatch.org/01QuackeryRelatedTopics/colonsuit.html
(Their mission statement, FYI: "Quackwatch, Inc., which was a member of Consumer Federation of America from 1973 through 2003, is a nonprofit corporation whose purpose is to combat health-related frauds, myths, fads, fallacies, and misconduct. Its primary focus is on quackery-related information that is difficult or impossible to get elsewhere. Founded by Dr. Stephen Barrett in 1969 as the Lehigh Valley Committee Against Health Fraud, it was incorporated in 1970. In 1997, it assumed its current name and began developing a worldwide network of volunteers and expert advisors. Our activities include: