Most overweight (MOST) have some sort of sleeping disorder due to being overweight. THIS is like Lisa said, noninvasive test. More annoying than anything else. The doctors need to know if you are apnea so when they are done with surgery, they can safely get your breathing under control using your preset CPAP machine. They want to ensure the BEST possible results for you and them. NOBODY needs your oxygen levels getting dangerously low! I have it, and I have a CPAP. I am glad to know this now, and have been using it since February 2013. GOOD LUCK!