This probably happens more than you would know, darlin'.
First of all, I wouldn't beat myself up about it. As many have said, you might want to mention it going into an appointment so she is prepared and can plan to be gentle in the early part of the appointment.
MY personal solution is to offer a nice, wonderful massage while chatting a bit to make sure you are relaxed and comfortable. By the time you turn over, we will worry about whatever happens at that point.
Now if you relax "too much" in the first "5 minutes" of the massage, then we have the rest of the hour to carry on with the massage and perhaps get you more relaxed again.
You book an hour with me, you get an hour...that is just the way I roll.
Good luck in your hobbying darlin'...I think you will do just fine.