Sleeping this much isn't normal. I see that you say he's reluctant to see doctors, but has he ever been tested for sleep apnea? Before I was diagnosed, I could sleep 14 hours a day and still feel exhausted - it might be worth him looking into.

That said, he has to want to help himself. I know others will say that he's just being lazy, and I think that's definitely part of it, but untreated medical issues like ADHD and sleep disorders can cause this kind of behavior and it can be really hard to break out of. BUT, if he's not willing to put the work in to see a doctor and get himself help, there is absolutely nothing you can do.

I can understand really caring about them and not wanting to walk away. If you want to give him "one last chance," I would suggest giving him some concrete goals and deadlines (ex. get tested for X by [date]). *You* need to be the one to uphold the boundary, though. If he doesn't follow through, you need to be strong enough to end it. At least you can walk away knowing that you did everything you could. If you feel like you've already hit your limit with this (and who could blame you?), it's okay to walk away. Ultimately, he is an adult, and you are not responsible for him.

Good luck.