Well, try to understand that you'll have some days where you feel energetic and focused as well as days of tiredness with brain fog. Today I think I could've sleep all day and still be tired. I got over 10 hours sleep and felt like taking a nap after I got up.

I know a guy who's on disability based on some sort of sleep disorder. (This is in USA.) If your doctors keep good notes, they should be able to support your case if you're denied.