First night of CPAP

Last night was the second sleep study. They fitted me with a CPAP and tested air pressure while I slept. It was mildly uncomfortable, but I didn't have any trouble getting to sleep. I scarcely remember waking up and the night whizzed by. It felt like a good rest. Back home after breakfast, intense drowsiness came over me. I went back to bed at 8:00 and slept another 90 minutes. What does this mean? Usually once I wake up in the morning, that's it; I cannot sleep during the day unless I'm sick. Maybe my brain missed being oxygen-deprived. I still have to wait another month to find out the test results and go shopping for a machine.