I've seen some "study" correlating diabetes with excessive sleep, but I'm unconvinced. It seems to me that diabetics and pre-diabetics would simply be more prone to crashing and sleeping too much, not the other way around. I can't believe that excessive sleep causes diabetes. By what mechanism? It makes no sense.
12 hours is not too much. I do well on ten hours, and twelve is quite alright also. I see no reason to limit sleep. Sounds like hell, actually, to want sleep and tell yourself you can't. That's suicide in my book.
If you aren't normally a long-sleeper and suddenly find yourself sleepier than normal, then maybe something is going wrong somewhere, nutritionally or hormonally, socially, etc. But for people like me who naturally sign on for a good 10-hour stay in bed-land, it's just nature. There is no one perfect sleep pattern which applies to everyone.
Steak, eggs, potatoes - fruits, nuts, berries and forage. Coconut milk and potent herbs and spices. Tea instead of coffee now and teeny amounts of kelp daily. Let's see how this does! Not really had dairy much, and gut seems better for it.