Guys, I have a problem, can somebody help me?

Hi guys. I have an issue rn and any comment helping is something I'll be very thankful. 

My long distance boyfriend is most likely to be hypersomniac, which means he must sleep 12 or more hours to be fully rested. This is a side effect of the depression he had years ago, and due to this now he has a very different sleep schedule which means he sleeps during the day and is awake at night.

I didn't have an issue at first with this, because he had a sabatic year of studies and we also entered in vacational breaks, but now he is in the second year of his studies and has to do an extra semester just because he dismissed the most of the classes because of the sleep schedule... and also it started to affect me physical and psychologically talking. Plus, that this issue also started to affect the moments we are together, making him fall asleep as a baby when we have to do things or even getting late at places because he was asleep.

I tried everything: talk to him, encourage him to have a healthy sleep schedule, tell him to book an appointment with a sleep specialist, book an appointment with a doctor, tell him to go to sleep... everything.

Do you guys have any tips? How can I help him? Please, I'm desperate, I don't know what else to do, and this worries me so much.