Can't wake up

I would suggest that he talk to his doctor about having a sleep study done. He'll spend the night in a sleep lab where they'll hook him up to monitors and measure his sleep patterns. He could have sleep apnea- where he stops breathing for short periods during the night. (If you allow him to fall asleep before you do, you may be able to notice this.) He could also have narcolepsy or be sleep walking.
One other thing that might help, in case he doesn't have a sleep disorder: make sure your curtains are light enough to allow natural light into the room. This won't help if he gets up before the sun rises, but if he needs to be up later, the sunlight helps to 'tell' the body to stop making melatonin and wake up. I hope this information helps you out.

Does he have low blood pressure?
Sleep apnea was another thought (I see the above poster mentioned that)