My dad has been on a lot of different medication for arthritis in his hands, also for severe heartburn. But the doctors have ruled these out for causing this sleep problem. He's had every single test from blood tests to checking for diabetes but still no one knows why he does this..

He can sleep forever. If no one or nothing wakes him up, he just will not wake up. Last sunday morning he got up about 11am and came into the sitting room, he sat down and within 5 minutes he'd fallen asleep again. As i'm typing now he's asleep on the settee, but he isn't lying down.. He's fallen asleep almost instantly of sitting. Work uniform still on and tv remote in hand. When we're at friends houses my mum have to keep an eye on him because he tries so hard to stay awake but finds it impossible (and that's highly embarrassing and extremely rude when you're at someone else's gaff). Does anyone know what could be causing such a bizarre sleep disorder. (he's obviously got some sort of narcolepsy but the incompetent doctors from where I live can't see it)