Second sleep study in a few weeks

My first sleep study was a couple of weeks ago. When I awoke, I asked the nurse how things looked. She said that things looked pretty good, my oxygen levels were at 94% but she didn't have time to monitor my study. I figured that I was not experiencing sleep apnea. To my surprise, I received a phone call from the sleep lab today to schedule a CPAP sleep study. Does this mean that I in fact do have a sleep disorder, or is it common practice to have two sleep studies, even when the person does not appear to have a sleep disorder present?

Second study is for titration--determining what pressure splints your airway enough to stop/prevent your apneas.