To me, if it was caused by stress he'd more likely be tossing and turning, thinking about
stuff, getting out of bed, not sleeping, etc. He said he's asleep 6.5 - 7.0 hours a night but wakes up tired. Classic symptoms of sleep apnea.
I have a machine I don't wear as well.
I think specialists can check people now for that without going for an overnight stay, like I did. That'd be my first course of action.
I've been stressed because of a job, teenagers, money, women, etc. There's a difference in not being able to sleep and feeling bad after sleep, in my opinion.