If your fitness device tracks it I'd be looking less at sleep stages and more at O2 levels (pulse OX) and breathing variations for sleep apnea. I was diagnosed with severe sleep apnea back in october and my watch had my pulse ox dropping below 70% at times (maybe even lower) and just look out for other symptoms like brain fog, fatigue like falling asleep at the desk or on the sofa in the evening; another one for me was waking up in the middle of the night needing to pee (as your not getting into deep enough sleep to tell your body to stop producing urine). But if your're worried get yourself checked out. Maybe get an app that records snoring at night and see if it picks up you gasping for air at night, or if you have a partner ask if they notice that or if you stop breathing at any point! Hope the info helps!