A sleep study is critical to ruling out sleep issues before getting a proper diagnosis of ME/CFS. No good doctor would diagnose CFS without a sleep study.
That could rule out apneas but not the overall possibility, based on typical sleep studies anyways. e.g. you regularly go to bed thinking about the stuff you have to do tomorrow, so your brain doesn't enter deep sleep phases for long; your doctor thinks 6-7 hours of sleep is good, when you in particular need more like 8.5 ; your neighborhood is noisy, etc.