It could be all of the above. I was diagnosed with "mild" sleep apnea and a CPAP hasn't really made an improvement on my day-to-day.
The main difference is that occasionally I used to wake up feeling completely hung over and near death, and now that no longer happens if I'm using my CPAP.
Most days, I am still tired - I am learning that is probably due to depression/anxiety (working on treatment now), ADHD (can't treat it until the former is stable), and poor stress management (undiagnosed autistic kid with zero social/emotional support).
The problem with CPAP is that it prevents full airway collapse and apneas very effectively, but often just converts them into subtler collapse ending with arousals. It also introduces its own disruption through expiratory resistance, reducing arterial CO2, patient-ventilator asynchrony if you're using any EPR or bilevel features, etc... bleh.
The main difference is that occasionally I used to wake up feeling completely hung over and near death, and now that no longer happens if I'm using my CPAP.
Most days, I am still tired - I am learning that is probably due to depression/anxiety (working on treatment now), ADHD (can't treat it until the former is stable), and poor stress management (undiagnosed autistic kid with zero social/emotional support).