I have heavy fatigue and tiredness. been trying to rest and even ended up falling asleep at 18:00 earlier this week and slept 12 hours straight. not sure if i should be concerned?

You did not mention what you do every day that might make u tired. Sounds to me like U might be doing too much. Go to uptodate.com and read about OSA and good sleep habits. Discuss with your team.

Fatigue is one of those symptoms where the list of reasons for it is pages in a medical textbook. I could not address this without more information.