My husband used to sleep at least 10 hours a day and sometimes 11 or 12 and it had me very concerned because i didn't want him to miss he morning meds, i didn't want him to become dehydrated AND he needs to eat, right? So, I just let him sleep, cuz he can be a grumpus when I wake him up.
I told his neurologist about this and she said not to be too concerned about his 9-12 hours of sleep because his mind is resting and he doesn't have to "think or remember" anything, which made sense as soon as she said it. He was also taking naps here and there, but not every day. She told us to "break up" his sleeping cycle but still let him get his sleep and/or naps.
I ended up getting a little creative, so when he wakes up in the morning, to maybe go to the bathroom, I have him take his meds before he gets back into bed for his "morning nap". Then I gently wake him up a few hours later to eat and get him dressed.
His doctor pointed out to him that he needs to be up and awake when the world and people are moving around and to get fresh air when it's daylight. He's not sleeping AS much as he used to which I am thankful for. So maybe it was just a phase for now. Don't know if he'll ever go back to those sleeping habits, but if he does, at least I'll know why.
There might be other reasons for his sleepiness or fatigue so make a journal and talk to his doctor about it.
Love and Prayers to you