What Happy said reminds me of something I read about the creams - both diltiazem and rectogesic. That they can be absorbed "too quickly", producing side effects, and so they recommended not applying them right after a bath (better to wait 30 minutes), because otherwise they would be taken up too quickly. I think that was somewhere in the References section.
Hope you feel better soon...

Thanks everyone for 'sharing' this with me. Makes the pain that much more bearable.