What can I expect (and how can I keep relaxed) during a desert hot stone mage?

I'm getting married this weekend, and decided to treat myself and my future sister-in-law (who has to be in the room with me and vice versa for each treatment since she's under 18) to a day at the spa this week. We're both getting desert hot stone mages, and were told that a robe is provided, but that we should be naked under the robes, and during the mage and purifying seaweed body wrap we're getting. I'm shy, and a little intimidated by the fact that I have to be naked in front of my future sister-in-law and the meuse. Does anyone have any tips on what to expect, how to stay relaxed, and not freak out? I want to enjoy myself and keep from worrying that the meuse thinks I'm a wacko.