I am assuming I have the right kind. It hasn't failed me yet.
The reason Dr. Clark wants you to lay on your side is to help push the stones. I may be wrong, but if my memory serves me correctly, it's just a few minutes she wants you to do that. But, I will add that some people do NOT lay on their side and they get positive results, too. (They have published their posts on this forum) So, decide what is best for you!